with grief. it was a tragedy. but for lisa's dead, a sheriff's deputy it was no mystery. he was sure he skbu where the killer was. a neighbor with a gun and a grudge. >> i thought they better get there before i do. >> some said the couple was having trouble. that seth has secret. >> did she tell you she sent topless pictures? >> someone said it's right under cops' noses. a case unfolding on camera, one nat would stes three jures, shatter two families. and chase one final twist. >> that was her biggest secret. ♪ the corn fields of iowa are a far place from memphis. but it was here a baby girl was named after a princess. lisa marie. yep, that one. >> as a kid, i was pretty big-to elvis. i knew my first daughter was going it bow lisa marie, because of elvis,f course. >> she was the life of the party. >> once she started talking, she haddent shut up. >> tracee and todd caldwell watched their girl grow up all but unstoppable. bowling time. weir not talking saturday night? >> no, anything she did she had to be the best at it. >> a lisa was a teenager when they divorced. all the while he was working as a deputy in the sheriff's department. he found comfort in several ways. head take out his sketch pad from time to time and then he met and fell hard for a nurse named aidan. before long, he was starting father hood all over again, this time with twin daughters. he was getting a lot of help from the twins. >> she was more like a second mom to the twins than a big sister. >> they were close relationship? >> uh-huh. very. >> i would get into bed with her and we'd watch old episodes of "the golden girls." she says i'm dorothy because i'm such a grouch all the time. that was my favorite time with lisa. >> i'm so lucky. >> but step mom, amy, put on her enforcer hat when it came to her teenage romantic life. >> i wanted to know who the boyfriends were, who their parents were. i was the one they had to pass the test with. >> the boyfriend we had passed with flying colors was a kid named seth techal. he came from a long-time local famalty. his father had been the mayor. mom a social worker and dad owned the local bowling alley. that's when seth began noticing lisa. his dad was her high school coach. and bowled almost but not quite as well as lisa. they worked part time together on the lanes. that was becoming boyfriend and girlfriend. you liked this young girl? >> a lot. yeah. >> see the was a part of our family. >> they were a church-going family and seth's mom remembers how the boys' compassing for others shown on a relief mission to mississippi. >> he talked to these folks for hours and hours and they became really good friends. i have a lot of memories like that of seth. >> helping people? >> yep. >> and lisa wanted to help people too. she followed her father into law enforcement. >> i told her she would have my blessings if she was pt just an average cop. i didn't want to have to worry about her inefficiencies maybe endangering her life. >> after years of hearing patrons joke about whether the tw of them were going to get married, jeff and lisa made the inevitable official. >> seth came to our house and met with us and asked our permission to marry lisa. >> old school? >> old school. >> after dating for years, they got married in october 2011. she was 22, he was 21. >> i told him no matter what he did to take care of her and protect her. >> and he said. >> he said he would. >> she got more than a brother in law in seth. >> he was my friend. >> he called me dad. we told each other we loved each other. i felt as close to him as i did my vun. >> for lisa, it was having all his buddies come along too. a package deal. how did lisa put up with you guys? >> she was kind of interested in the same things all of us wer. she liked to go hunting, fishing. >> sounds like you would be happy if she were your girlfriend? >> seth was lucky. >> but he knew it was time tool get a job. he signed on as a volunteer firefighter and drew a paycheck as a security guard. but his father in law was helping him with a soon to start job as a jailer for the sheriffs. >> they were very close. that's why i think he went into lieu enforcement. >> a new job, young marriage and more changes for seth. he was going to be a father. zoe maria. in may 2012, they were halfway through the pregnancy. seth and lisa, a baby on the way, were starting out their married life in this humble trailer. it was a gift from his dad. a kind of starter home while they saved money for the future. the only cloud was an escalating feud with an across-the-fence neighbor here. there was bad blood. it happened at 5:00 in the morning. a sudden horrifying sound that shattered two young lives. >> 911. what's your emergency? >> saturday, may 26, 2012, memorial day weekend. >> she's not breathing. she's been shot. >> reporter: a shotgun blast had ended all the plans of mr. and mrs. seth techal. coming up, >> i have a report of a lady not breathing. i have been advised that the lady has been shot. >> even though somebody could have shot at you? >> that was possible the whole time. hat was pauossible the who time o man, that's a whole lot of wrinkly at least my shoes look good! looking good start with bounce wrinkleguard, the megasheet designed to prevent wrinkles in the dryer. -hey. -hi. whoa, nice car. thanks, yeah. i actually got a great deal on it too, although my interest rate is awful. have you checked your credit? i got like a free score from some app or something like that. but lenders don't even use that score. creditrepair.com has a free credit snapshot that can show you exactly what's happening with your credit score. and killing my interest rates. well, great seats though. -thank you. -like really. just knowing your score won't improve it. instead, work to actually fix your credit with creditrepair.com. it was the ends of a long, overnight shift for sheriff's deputy, marty wonderland, the only deputy on duty in iowa. with the first hint of day break that saturday morning, marty relaxed and turned up the music in his cruiser. it's the ragged end of the shift for you. >> i'm taking my last loop around the county and go tooling watch the sun come up and go home and go to bed. >> reporter: that plan came to an abrupt end when seth made a desperate 911 call from his house. >> i've been shot. and shot in the side. >> dispatch relayed the question to marty wonderland. the young deputy had never got call like this. >> report of a young lady is not breathing. young lady's been shot. >> is your heart pounding a little? >> that's an understatement. >> with his car and his mind, both doing 90, marty raced to the house in under ten minutes. he slowed along the rise of the gravel country road and stopped in the driveway. his dashboard camera captured the scene as he approached the house. >> what do you see about here? >> you can see seth up on the porch. he's wearing cargo shorts and a belt and he's bent over. >> what's he doing? >> sounds like he's crying, just sobbing. >> the toughest call of marty's career was suddenly more complicated. he knew the grieving husband on the porch, considered him a friend and knew her too and the victim's father was well known deputy. this is the first time you've had major crime and also people you know. sdwlilts tough. >> were you scared? it's okay if you were? >> definitely was scared. concerned about a lot of different things. >> didn't know if someone was going to shoot at you? >> that was possible the whole time. >> the possibility of a live shooter still on the grounds, marty's adrenalin was pumping. when he entered the trailer a paramedic was tending to lisa. it didn't look good. marty's only thought was to help her but he had to secure his rifle. so, he ran back to the cruiser. >> in mind site, i wish i wouldn't have done that. >> why? >> because i saw a lot of things and now because i asked him to come out there, i he has to livable with some same images i have to livable with. >> we get a call from a dispatcher i've known for 20 years and i can tell his voice is different. from what i remember, he just said you need to get to lisa's house. she's not breathing. >> he bolted out of bed. >> i didn't put shoes on, didn't put socks on. i went in my pajamas and road 90 miles per hour. i'm an er nurse. >> you're in nurse mode? >> i'm thinking maybe if i get here fast enough, there will be something i can do. >> todd raced behind in a separate vehicle. >> i repeated over and over, oh, my god, oh, my god. frrt that's all i could think and say. >> at the scene, deputy ran back to the house and did what he could to help the emt. >> started giving lisa cpr. it felt like forever. and i'm asking him you want me to do cpr still? and he told me not to. >> there was nothing more to do. she was gone along with her unborn daughter. lisa marie was just 23 years old. >> i ran in there and you could tell she was gone. >> so, you went into the bedroom and saw her. did you tend to her? >> yeah, i held her hand and i rubbed her belly and i just said my lisa, my leashau. >> todd, did you go into the houses to help her? >> yeah, i did. i went in there and i seen her laying there and i seen the amount of blood that was on the bed and i knew, from my experience, that was too much blood to sustain life. when i listen on the tape recording of it, i hear myself bellowing. i don't know how to describe it. i don't even remember doing that. >> what happened? [ crying] >> it was a heartbreaking scene but deputy marty wonderland had a job to do. you're in the barrel here. >> got to start working it. >> there was an immediately, from of all people, todd caldwell, said he knew who the shooter was and in a voice filled with rage, he told his fellow deputies to take the suspect down. >> go get him, go get him, now. >> coming up, who was todd caldwell talking about? turns out there was someone in seth and lisa's life who had everybody worried. >> things were escalating. they thought they could handle whatever but they were fearful, i was fearful. >> did you think he was a risk? that this is a guy capable of flipping out? >> i did. capable of flipping out >> i did namaste... ...surprise parties. aww, you guys. dupixent helps prevent asthma attacks... ...for 3!... ...so i can du more of the things i love. dupixent is not for sudden breathing problems. it's an add-on-treatment for specific types of moderate-to-severe asthma that can improve lung function for better breathing in as little as two weeks. and can reduce, or even eliminate, oral steroids. and here's something important. dupixent can cause serious allergic reactions, including anaphylaxis. get help right away if you have rash, shortness of breath, chest pain, tingling or numbness in your limbs. tell your doctor if you have a parasitic infection, and don't change or stop your asthma treatments, including steroids, without talking to your doctor. are you ready to du more with less asthma? 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>> yep. >> seth was inconsoleable and acting out. >> i went over to him when i first got there and i tried to hugging him. he pushed me away. he punched his truck and i said don't do that, soegt. let me see your hand. >> todd offered to take seth back to his house. >> it was just bad. he was sobbing and we just hugged and cried. >> marty wonderland, working his first homicide was the first deputy to speak to seth. >> through the husband sobbing, a story started to emerge. >> basically tell said me he was in the shower getting ready it go to work and hears a gun go off. >> down the hallway. >> some sort of intruder? >> yeah, someone came in while he was in the shower and shot lisa and got away before he could catch them. >> we'll figure it out. >> lisa's father, todd, thought he had it figured out and already had a suspect. >> go get him, go get him, now. >> todd's rage was directed at the neighbor on the other side of the fence. a 56-year-old army veteran, named tate. >> i thought they better get to him before i do. >> reporter: ryan tate was embroiled in an escalating feud with his neighbors. todd knew about it and was certain his daughter was dead because of it. the culmination of bad blood? >> right. >> reporter: started about two months before the murder. seth pulled a dead deer off the property line. ryan tate later tossed the hide on to seth's property. seth tossed it back and the war was on. todd caldwell responded to one in april and tate pointed the finger at his young neighbor. >> i can't remember their names. >> seth techel. >> techel? >> yeah. >> they're good people. they really are. >> this guy, brian tate, does he know you're the father in law of the neighbor? >> no, and i don't want to tell him that because i don't want that to effect maybe what he does or doesn't do. >> and he thinks that's the source of the trouble, the people opening the trailer across the way? >> yeah. >> ryan tate told todd feces had been hurled at his home. he described the vandalism in stark terms. >> he says he thinks these are acts of terrorism. kind of bell goes off like terrorism's kind of a weird word to use. and halfthal time, i notice a shotgun laying on the ground. and i'm like that makes me >> twitchy? >> yeah. exact le. warning about tate that he might be dangerous. >> i'm thinking i don't want to be the reason the deputy goes out there and goats hurt. be careful tate may be 1096, which means mentally challenged. >> tate had been diagnosed as a paranoid schizophrenic. seth's mother was worried. >> she was terrified. this was when things were escalating. they thought they could handle whatever but they were fearful. the i was fearful. >> on may 15th, 2012, just 11 days before lisa was killed, an agitated tate made another call saying the vandalism got worse. >> i'm trying to have a conversation with you. >> i don't want to be yelled at either. >> i'm trying to have a conversation with you and i don't understand why you walked off. >> you raised your voice. >> you're right because you're not listening to me. >> did you think this was a guy capable of flipping out? >> i did. >> and now lisa was dead and the trailer was a crime scene. marty wonderland, the first deputy at the scene knew all about brian tate and zeroed in on him as his candidate for prime suspect. so, all the attention is heading across the fence to ryan tate? >> it is. >> reporter: they armored up and got out their long guns, not knowing what their suspect might do. you're ballsy enough to walk in and shoot lisa, you're ballsy enough for just about anything. did you put your body armor on? >> yes. had the red dot turned on. if things popped off, we were ready. things popped off, we we ready. to severe crohn's disease. then i realized something was missing... ...me. my symptoms were keeping me from being there for her. so, i talked to my doctor and learned humira is the #1 prescribed biologic for people with crohn's disease. humira helps people achieve remission that can last. and the majority of people on humira saw significant symptom relief in as little as 4 weeks. humira can lower your ability to fight infections. serious and sometimes fatal infections, including tuberculosis, and cancers, including lymphoma, have happened, as have blood, liver, and nervous system problems, serious allergic reactions, and new or worsening heart failure. tell your doctor if you've been to areas where certain fungal infections are common and if you've had tb, hepatitis b, are prone to infections, or have flu-like symptoms or sores. don't start humira if you have an infection. be there for you, and them. ask your gastroenterologist about humira. with humira, remission is possible. learn how abbvie could help you save on humira. o man, that's a whole lot of wrinkly at least my shoes look good! looking good start with bounce wrinkleguard, the megasheet designed to prevent wrinkles in the dryer. i'm dara brown. a fourth coronavirus wave appears to be on the horizon. americans are seeing long testing lines as the u.s. is averaging 124,000 cases a day, led by a surge of delta and rise of the new omicron variant. and palmer, one of the men who stormed the capitol january 6th was sentenced to 63 months in prison for assaulting police officers that day. palmer said he was horrified and devastated by his actions. it's the longest sentence so far for those charged in the attack. now back to "dateline." ♪ >> on the main street of tiny agency, iowa, bad news travel fast. a pregnant woman dead and a gunman on the loose. just as quickly fear took to roost. >> the 23-year-old reserve sheriff's deputy ways shot and killed in the town of agency. see was five months pregnant. >> lisa's murder was the first in the farm town in 15 years. and deputy philip. s had a personal stake in cracking the case. lisa's dad is one of his best friends. >> todd and i began the same year at the sheriff's office together. i reassured him we'll figure this out. >> whatever happened is within your family, the law enforcement family of the county? >> a right, we know everybody's kids and extended families. >> reporter: and knew something about the guy next door, ryan tate. ever since the first deputies arrived at sunrise, they'd been peeking across the barb wire. were they another shotgun blast away from finding out? at 1:00 that afternoon, eight hours after lisa was shot, deputy phillips and a team of investigators were ready to confront the neighbor. so, the decision is made we have to talk to ryan tate? >> definitely a purse often interest we need to talk to. >> did you put your body armor on? >> i did. >> marty wonderland did too. >> we're all strapped up. we're all ready for business. >> reporter: deputy phillips and a partner drew line of fire detail, approaching tate for an interview. ? he's our prime suspect. for it's very possible in all of our minds that he just shot and killed lisa. >> reporter: marty and the chief deputy provided cover in the driveway. >> had the red dot turned on. if things popped off, we were ready. >> nerves screaming, everyone was poised for battle, everyone, as it turned out, except for brian tate. he wasn't armed or belligerent. >> he was accommodating and got chairs. and we sat down in his front yard. >> in the front yard, in lawn chairs, his mother and brother by his side. no shotgun in sight. so, the cops turned on a recorder and started asking questions. >> you asked where are you? >> yeah. he said he was sleeping off a higher dose of medication for his schizophrenia. >> i went to bed about 8:30. >> right after i did. >> fell right asleep, didn't hear nothing, didn't get up till 11:00. >> reporter: she says he was still asleep with-the shooting must have happened before dawn. tate 's mother cooperated the alibi, although they know mothers can be biassed witnesses. >> i have was in bed and normally i would have been up, doing guard duty with all the stuff that happened but i'm schizophrenic paranoid. >> he called himself a sergeant major and walked a picket on his property line. ever since his property littered with dog feces and his barn pelt would rocks. he knew about the vandalism complantd he filed. they were the deputies that responded just 11 days earlier. they down played the complaints and thought he was off his meds. >> you said you'd sit outside here at night. when is the last time you did that? >> a good week or so. they don't want me to do guard duty anymore. they want me to get sleep, take more medications. >> he was such a calm, quiet guy until this vandalism started and then you're a different person. >> i was mr. nice guy for a long time and it did me no good. people took advantage of me. so, i'm taking a different approach to life right now. prrgs being more serious and not such a nice guy. >> after venting about the vandalism, the 40-minute interview was over. but investigators weren't done. they'd be back to question tate again. what did you think you had? >> we still had a who done it in our minds? >> but lisa's step mom and sister had no doubts whatsoever. >> i thought it was brian tate. >> reporter: but investigators knew they still had to talk to the husband. when they scheduled an official interview with seth that same day, it didn't sit well with amy. >> is this how you always treat grieving husbands and i started crying? i'm thinking they're being so mean to him. >> we got in an argument because i'm like they have to do that. >> seth techel knew the spouse had to be ruled out. said he was eager to get crossed off the list and instructed his parents no lawyers. >> i remember saying do we need to get a lawyer? >> he was adamant, i didn't do anything. i have nothing to hide. >> i don't need a lawyer. >> was that a mistake? seth had told his story to one familiar face after another at the scene but now he'd talk to an elite state interrogator and the tone of the investigation was about to change. >> coming up. >> that's fine. i know i'm obviously probably number one right now. >> deputies learn seth may be hiding something. what was the story you told in court? >> that seth had a track phone. e gives you two times brighter skin. hydrates better than the $400 cream. facing expensive vitamin c creams with dull results? olay brightens it up with new olay vitamin c. gives you two times brighter skin. hydrates better than the $400 cream. thinkorswim® by td ameritrade is more than a trading platform. it's an entire trading experience. with innovation that lets you customize interfaces, charts and orders to your style of trading. personalized education to expand your perspective. and a dedicated trade desk of expert-level support. that will push you to be even better. and just might change how you trade—forever. because once you experience thinkorswim® by td ameritrade ♪♪♪ there's no going back. ♪ todd and amy return home, destroyed and the longest day of their lives wasn't even half over. >> my remaining kids, i knew they were going to be horrified. i don't think of myself at that point. >> he was thinking about the son in law he loved like his own boy. seth agreed to go downtown without a lawyer for a formal interview. they called in deputies from the division of criminal. providing forensic resources and expertise and the deputies offering local knowledge and man power. dci's tony birmingham hand picked tomes to interview seth. >> there was no doubt in my mind that he was the one to do the interview. >> we only get one shot and have to be prepared for information collecting or that this could be our suspect. >> only eight hours after his pregnant wife was murdered, the interview got underway. >> in the interview room, agent thomas was in white. it started routinely. seth had already given his account twice to deputies at the scene but this would be his first time on videotape. his story begins somewhere around 5:00 a.m. >> exactly. >> i wasn't in there for more than five minutes and i heard this loud noise. >> he said he thought it might be a gun shot. so he jumped out of the shower to check on lisa, heard her moaning and said he grabbed his handgun from the night stand by the bed. >> i'll be honest i had every intention of shooting somebody. i ran back inside and said lisa, lisa, are you okay? and she's not breathing. >> during the interview, seth sometimes seemed overcome by emotion. [ bleep] >> why can't they still be alive? why? why? why couldn't i have done something to protect the woman that i love? >> the agent asks seth what he thought happened. >> that's the only thing. that'g >> seth then bolstered the cop's leading theory of the crime so far. that the neighbor, brian tate, had shot lisa. >> who was the first person that came to your mind? >> tate. crasisy -- crazy neighbor who thinks we're terrorists. >> talked about the deer hide and thought tate threw it over the fence so he responded in kind. escalated for several weeks in which tate said dog feces and rocks were thrown on his property. for that brought deputy caldwell out to the house for the official vandalism complaint. >> he says tate was rubbing a shotgun. >> seth says he knew the 10er of the visit because todd filled him in later. and his father, todd, gave him a strong warning. >> if you're doing anything to his yard, knock it off if your buddies are doing anything to his yard, knock it off. do not mess with this guy. he's off the rocker. he's going to be the next person to shoot a cop. i won't mess with him. i'll make sure nobody else is. >> reporter: he asked about the firearms he kept in the trailer. maybe one of those had been used. >> any guns had been missing? >> i havent looked. >> i just asked him to write down the guns that are in his house and he writes them all down. >> inevitably the agent turned to the sharp-edge intrucive questions that he has to answer. wanting to be a cop, he knew what was coming. >> i know i'm probably number one right now. >> let's talk about people in your lives. was there any extra marital affairs? >> no. >> seth didn't hesitate. there were no other women. but how did the trailer, quite unexpectedly, someone was about to put the lie to the rosy marital picture. a good friends had walked up to the crime scene tape. he told deputies and agents that he came to pick up the puppy they bordered him for. they began peppering the young friends. a detail that tumbled out surprised them. >> i told them seth had a track phone. >> a secret phone? >> yeah. he had been talking to a girl. >> the investigators had no idea where this would lead. but the unexpected revelation that there might be a girlfriend in the mix, meant they had to geten the horn with agent thomas downtown and praunto. seth was in the interview chair but could walk at any moment. coming up. more about seth's secret phone. seems it wasn't just for talking. >> did he tell you she sent topless pictures? >> yes. sent topless pictures >> yes ♪ when you have nausea, ♪ ♪ heartburn, ingestion, upset stomach... ♪ ♪ diarrheaaaa.♪ try pepto bismol with a powerful coating action. for fast and soothing relief. pepto bismol for fast relief when you need it most. ♪ after a night like this, crest has you covered. crest, the official toothpaste of santa. follow us @crest to celebrate the 12 days of crest smiles. ♪ seth techel had gone downtown voluntarily but now his interview dragged on for a couple of hours. his father grew concern. so, he called in a lawyer to bring the questioning to a halt. >> we called the sheriff's office and said we have a lawyer waiting to see seth. >> but inside, seth kept talking away. he was oblivious to the fact thatthal interviewer was getting real time from the crime scene. >> i got a text. >> the friend with a puppy. >> and the friend told us a story about a girl named rachel. >> but agent thomas held his fire, in part because the information was still limited. seth, however, likely could see the agent reading a text. husband, father to be, who answered an emphatic no to the question about an affair, made an admission. >> there's a female from work i was techting. >> said her name was rachel macfarlane. he said even lisa knew about it. >> i wasn't seeing her. just hey, how was your day kind of thing. >> sexting? >> none of that. >> what are you wearing? >> none of that. rachel found out everything was kosher. i stopped talking, you know. we got over it. >> we have to be honest about her, okay. is there anything you haven't told us yet? >> no. everything is going to add up the way i told you. >> rachel 's dna on your clothes? >> i never had sex with her. nothing oral, nothing like that. i gave her hugs and i kissed her. >> by now, seth's father and attorney had arrived and were trying desperately to end the intervau. but it was after hours and the outside door was locked. bang, bang, bang on the door. is that you? >> that's me. that's me. >> they wouldn't stop. they didn't come out. >> they didn't have toop to. remember, he was advised that he was welcome to leave any time. and he simply ignored the commotion outside. >> i did get information they were wanting to get in and tell seth to stop talking. >> shut you guys right down. >> seth is an adult and he had a sole obligation to invoke his right to an attorney. >> so, he kept asking questions and seth kept answering. >> ever lie to her about rachel? >> no, she found out and that was that. >> reporter: meanwhile, they learned more details from seth's best friend, the guy with a puppy. he explained seth was using the special track phone as a steamy hotline. >> i know they were exchanging photos. >> did he say she sent him topless pictures? >> yes. >> did he show them to you? >> yes. >> did colten know about you texting rachel? you tell him about it? >> yeah. >> this is an ongoing investigation. and it's up to you to be honest. >> there's obviously more to the rachel thing. see was under the impression lisa was going to pack up and leave. >> he said he talked to rachel about leaving lisa at work. >> she asked if i was going through it with but obviously i lied. >> said he was stringing her along. >> i wasn't going to leave her. >> reporter: lying to rachel was wrong butted said lying in the interview was simply a way to spare his father in law the embarrassment. >> this is something i didn't want todd to find out. >> the interview had been going on close to four hours and agent birmingham was aware that seth's father and a lawyer wanted to shut them down. agent thomas took a break. met with birmingham and they decided he had to go nuclear. be confrontational because if we're going to be tough, now is the time. >> now is the time. >> here's the deal. facts right now, these case facts show us you're responsible for killing your wife. >> no, no, i'm not. no. i can't kill my wife. i can't do it. what facts do you have that i killed her? >> listen, i've seen rachel, okay? i know what you guys see when they see her because i see the same thing o cay? >> i'm telling you. if i wanted to be with rachel, i would get a divorce. i would not [ bleep] my wife over something that small. you know what, right now, i guess i don't give a [ bleep] what happens. i know what happened. i know what you're trying to to. you're trying to get me upset and it's working. congratulations. >> seth said he'd had enough and strangely shook thomas's hand and then he walked out. in the end, what did the investigators have? that seth lied about sex but was it even that? all he admitted to was making out to rachel and he insisted over and over again that he he did not kill rachel. even agent thomas expressed disappointment with the outcome of the interview, nearly five hours long. you felt like you came out affa 15-round fight? >> felt somewhat like a failure. >> why? >> we didn't get the full confession. >> maybe that's because seth didn't do it. agent thomas just didn't know. but the women in the caldwell family, without knowing any of seth's admissions about rachel believe with 100% certainty he did not kill lisa. >> i was never thinking that seth did it. >> only todd caldwell was no longer a true believe. but the question why seth needed to lawyer u his own investigative instincts kicked in, although he asked his deputies not to tell him anything until they knew something. >> i would say neither seth nor brian tate were completely liminated as suspects. >> at that time they were meeting to take stock. they knew they had a husband with a possible girlfriend. and a maybe crazy neighbor with a vendetta. but they also learned by that night there was a missing shotgun. what did it all mean? coming up. one piece of the puzzle falls into place. >> that was huge in the case. >> it was. >> and then another round of heartbreak for lisa's family. this is more than your brain can absorb? >> definitely. >> when "dateline" continues. >> when "dateline" continues is. so is screening for colon cancer. when caught in early stages, it's more treatable. hey, cologuard! hi, i'm noninvasive and i detect altered dna in your stool to find 92% of colon cancers even in early stages. early stages. it's for people 45 plus at average risk for colon cancer, not high risk. false positive and negative results may occur. ask your provider if cologuard is right for you. 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>> i think he was just shocked. >> that sunday wasn't a day of rest for the men and women trying to solve the crime either. investigators were focusing on the murder weapon and were working a lead on a .12 gauge shotgun. it belonged to seth's roommate who had just moved out. we showed lucas this photograph taken of seth at his home. if you look in the upper right-hand corner, lucas, the gun rack. >> yep. >> is your mosberg in that slack? >> yes, the middle one. >> lucas talked to deputies about the gun on the day of the murder. >> i told them it should be there. >> reporter: it wasn't there when crime scene techs scoured the trailer. and cops knew another place it wasn't. on the list of guns kept at the house that seth had written out for the dci agent. investigators felt certain the mosberg was used to kill lisa, but a big question remained -- >> where is it? that's what we want to know. where is the gun? >> that same sunday a team began searching the big, beautiful piece of property where seth and lisa were starting married life and preparing to raise a family. deputy marty wonderman working his first-ever homicide case was back at the search. over here by this tree, what do you center. >> "we've got it, shotgun here," they were going nuts. >> there of the mosberg in the tall grass about 20 yards from the back door of the trailer. that was a huge development in the case. >> it was. i think everyone's mood doubled or tripled when they found the gun. >> ballistics would match it with the slug that killed the pregnant lisa. investigators could fill in one big box on their checklist -- murder weapon. next they worked on possible motives. was it a neighbor with a vendetta or a husband lusting after another woman? state agent birmingham and deputy phillips decided to have a talk with seth's work friend, rachel. >> we interviewed her on tuesday, may 29th. no tricks here, someone has lost their life. two people have lost their life. >> reporter: over the course of two hours, birmingham and phillips peeled back the layers of rachel's relationship with seth. >> they were having kind of an ongoing relationship. there are sexually explicit text messages, pictures, sexually explicit pictures sent back and forth. >> he kissed me, but it never went to anything else. he used to tell me "i love you," that's about it. >> reporter: it sounds like they were making out rather than having sex. >> yes, that's correct. >> he always used to tell me how pretty he is and how he'd like to be with me. i always made it clear that he's married and has a wife and he's having a baby, and i don't wreck families. >> reporter: rachel told investigators the seth she knew couldn't be a murderer. >> would it surprise you? >> honestly, yes, it would. >> reporter: seth was a suspect. if he did fire the shotgun blast, that would place rachel at the heart of a murderous love triangle. >> i think that's why i feel so guilty because i don't want it to be because of me. >> reporter: the next day, deputies phillips and wonderland were back at the neighbor brian tate's house. this time they asked hip pointblank about the murder of his neighbor. >> we're trying to figure this out. did you have anything to do with the murder? >> no, i didn't. >> reporter: tate stuck to his alibi -- home and asleep after taking his medication. lead agent birmingham thought he was telling the truth and crossed brian tate off his suspect list. you only have one suspect at this point. >> one suspect and only one suspect. >> reporter: that evening, lisa's loved ones gathered at a funeral home for the visitation. the turnout was impressive and included many of todd's friends in the sheriff's department. your fellow officers are there as they would be, you know, pay condolences, show respect. >> right. right. >> reporter: the mood inside was somber and uneasy. the caldwells gathered near lisa's coffin. the techels stayed in the back of the room. seth was there. his sister-in-law was never forget what happened next. >> he actually came up to me kind of in the middle of it, gave me a big old hug, and he said, "you will always be my little sister, and i love you." i was like, "i love you back." >> reporter: when the last visitor was gone, only the two families remained. still at opposite ends of the room. >> i saw the two dci agents come and sit down been me. a couple rows behind seth and i. i said, is this a personal visit or a professional -- >> reporter: or something les? >> he said, "it's professional." >> reporter: marty wonderlin was there. >> we asked seth to come outside. we did it quietly i thought. >> reporter: when they were outside, the deputy carried out his orders. he arrested his friend, seth techel. a fellow deputy put the cuffs on him. they were lisa's cuffs, the ones she'd used as a reserve deputy. this has got to be just more than your brain can absorb. >> definitely. yeah. >> reporter: little sister, i'll always love you. and now he's going downtown, he's about to be charged. >> yep. i couldn't understand it. we wouldn't ever dream or understand that happen it could be him. >> reporter: seth's dream was to drive a sheriff's car as a deputy. now the wannabe cop was cuffed, riding in the back seat, and about to be charged with the murder of his wife. coming up -- together techel goes on trial. but before it even starts, the prosecution suffers a major blow. >> bad for us, good for them. great for them. >> reporter: and then a clue you haven't heard about could change everything. >> i believe it to be the most compelling piece of evidence in the whole case. the whole case the peñas are saving big holiday shopping at amazon. so now, they're free to become... ♪♪ the party peñas. ♪♪ they see your ugly sweaters, and raise you some mittens. and that's just basic wavy guy maintenance, right? next up, carvana. oh, boy. carvana just doesn't seem to understand how the test drive works. they give their customers seven days. and if they don't like it, they give 'em their money back. wait, they take the car back? that's crazy! what if it was driven by like a zookeeper? or a mud wrestler? or a guy who's on the outs with the missus and he just needs a place to sleep for seven days? yeah. (vo) buy your car online. love it or return it. with carvana. frequent heartburn? not anymore. the prilosec otc two-week challenge is helping people love what they love again. just one pill a day. 24 hours. zero heartburn. because life starts when heartburn stops. take the challenge at prilosecotc dot com. i've been telling everyone... the secret to great teeth is having healthy gums. crest advanced gum restore. detoxifies below the gumline... and restores by helping heal gums in as little as 7 days. crest. the #1 toothpaste brand in america. for lisa techel's family it had been a heartbreaking, relentless week. thursday didn't promise to be any better. lisa's funeral was held at the first lutheran church. seven month earlier todd caldwell was at the same church walking his daughter down the aisle on her wedding day. now he'd returned to lay her to rest. lisa was buried in her jailer's uniform. a special detail of officers used as pall bearers. law enforcement had come to honor one of its own. >> lisa would have thought, you know, this was for me? i was so proud. >> i should have been able to be there and watch her become a mom. she was just a joy. >> reporter: mothers shouldn't bury daughters. >> never. never. >> reporter: after the funeral, the caldwell and techel families turned their attention to the upcoming murder trial of seth techel. lawyers started to plot strategy with the neighborhood, brian tate, expected to be right in the thick of it. tate's sister sheri says he never could shake the feeling that the authorities would come after him. >> he still feels like they're saying he's a murderer. brian had even seen in the paper that they were calling him a crazy and deranged neighbor. it just devastated him. >> reporter: that summer, brian tate tumbled into a downward spiral and never recovered. he died in september, 2012, just four months after lisa's murder. the coroner would think it was heart. >> yes. >> reporter: what does the family think it was? >> a heart. a broken heart. >> reporter: now the prosecutors from the state's attorney general's office worried that a jury might think the deranged deceased neighbor did it. their plan had been to call tate as a witness. >> on the theory that the devil you know is always better than the devil you don't, we wanted the jury to see mr. tate. >> reporter: but now with a trial date approaching, prosecutors had lost a key witness. >> bad for us, good for them. it's great for them. >> reporter: the long-awaited murder trail of seth techel was in the hometown otumwa. february, 2013, can you see yourself going into the courthouse? >> yeah. i remember. >> reporter: what do you two say to one another? >> we got to stay strong. >> reporter: the caldwells never wanted to believe seth killed lisa, but heading into trial, they were all now convinced that he did. even presley, once his staunchest supporter. >> there's really no other explanation for what has happened. >> when you left the techel residence, who was there? >> reporter: two prominent families, the caldwells and techels, once close in-laws, were now fiercely divided, camped on opposite sides of the courtroom. seth had pleaded not guilty. >> i was like just look at me, like i want to see in your eyes how you're doing. but he doesn't look at you. >> she was like my best friend. >> reporter: prosecutors called to the stand their emotional trump card. todd caldwell remembered his lisa. >> like everyone would tell me how much lisa and i are alike, and i would just tell everybody that she's the best parts of me. >> reporter: the prosecution had the burden of proving the charges. first-degree murder and nonconsensual termination of a pregnancy. what did you think your strongest fact was going forward? strongest part of your story? >> probably the most important single piece of evidence was the shotgun. >> reporter: ballistics showed the mosberg .12 gauge was the weapon and only he had access to it that morning, prosecutors argued. >> no murderer who wants to kill lisa techel comes to the more scene without the murder weapon. >> we argued the impossibility of his story. some unknown assailant breaks in and kills the wife, that he says he's going to leave. >> reporter: prosecutors called one of seth's young friends to show the jury, they said, just how deceptive and manipulative seth was. it was one of the boys turned out behind all the vandalism across the fence. he testified he was just following seth's orders. >> told us to go mess with his neighbor tate. >> reporter: how were you going to mess with him? >> fill five buckets full of dog manure and dump them on his property. >> reporter: remember seth had assured his father-in-law and the state agent who interviewed him the exact opposite. >> and i said, i'm not messing with him. i'll make sure nobody else is. >> reporter: looking back, that incident was what turned todd against brian tate in the first place. fixing the idea in his mind that his kids' neighbor was a der ranged, maybe dangerous prank. >> i'm going by what seth had told me about him. >> reporter: as for tate's complaint calls with deputies as captured on dash cam video, it became evidence for the prosecution. >> we feed the squirrels, birds, and deer. >> we were hopeful that the jury would see brian tate as we saw him. >> reporter: and they sawcentri. certainly not a killer. at last it was time for the state's star witness, rachel mcfarland, the other woman, to show up and tell her story. did you need the jury to like her? >> we needed the jury to believe her. >> reporter: rachel testified her relationship with seth started heating up in december, 2011, which was two months after seth got married. >> it became more sexual, asking me to send pictures or -- i don't know, just showing off my body i guess. >> reporter: on may 20th, 2012, seth and rachel met at a nature preserve where they took this selfie to remember their time together. >> i mean, he kissed me, touched me. he said that we had everything in common and that he had tried working thins out with lisa, and they just weren't work, and i was exactly what he wanted. >> reporter: she said seth repeatedly told her he was going to divorce his wife. >> did he say he loved you? >> yes. >> reporter: but rachel was hedging her bets. she told seth she was also interested in a co-worker named brandon who just happened to call her during her tryst with seth in the park. >> he started getting really jealous. >> so on the 20th when you were communicating with brandon, he said what? >> just give me two more weeks. >> did you ask what he meant? >> yes, he just repeated the same statement. >> reporter: six days later, lisa was murdered in her own bed. >> and here we have a motive that we can understand -- love, the whole relationship with rachel was evidence that was like a countdown to lisa techel's death. >> reporter: but defense attorney steve gardner countered, arguing the motive of an affair falls flat without the essential element -- sex. >> seth techel was being accused of murdering his wife for an affair that he was hoping to someday have. >> you never had intercourse with him? >> no. >> you've never had oral sex with him? >> no. >> never had your clothes off? >> no. >> and you kissed a few times. >> yes. >> is that a fair assessment of the extent of your romantic relationship with mr. techel? >> yes. >> reporter: the defense also didn't accept the state's take on the neighbor as a eccentric. >> the most compelling evidence involved the neighbor, mr. tate. he was mentally ill. >> i'm done talking to you -- >> reporter: and according to the defense, dangerous, too. the defense then hammered home the portrayal of the unpredictable anywhere by using todd's own complaint summary from that day. you're in the awkward situation of being their best witness. >> right. >> you believed he could become a danger, anyone who should respond to that residence again should use extreme caution? >> that is correct, i did. >> reporter: the defense theorized that tate entered the trailer through an unlocked door and shot lisa for revenge. the key defense evidence that suggested an intruder was a stray peanut butter and jelly sandwich in a baggy left on the back deck. >> there was a sandwich that would not have been there the night before that was there. >> reporter: critters should have devoured it, he argued. he told the jury it must have the killer's snack. >> i believe it to be the most compelling piece of evidence in the whole case. >> reporter: it was now up to a jury to decide, but it wouldn't be easy. coming up -- in the jury room, deliberations and drama. >> he started pounding on the door, want -- saying he wanted out of there, and we were in tears. i've been telling everyone... the secret to great teeth is having healthy gums. crest advanced gum restore. detoxifies below the gumline... and restores by helping heal gums in as little as 7 days. crest. the #1 toothpaste brand in america. i'm dara brown. here's what's happening -- pfizer announced plans to expand clinical trials of the covid vaccine for children under 5 after review found a low-dose two-shot regimen did not produce the expected results. results are expected in the first half of 2022. former minneapolis police officer kim potter took the stand friday tearfully recalling the moments that led her to killing daunte wright after she mistook her firearm for a tieser. she faces first and second-degree manslaughter charges. closing arguments begin monday. now back to "dateline." back in the deliberation room, wrangling jurors in the trial were driving the case into a ditch. they stay you on and the stay out and stay out, what are the prosecutors telling you? >> that there's some that are guilty and some that are not guilty. and they're just not agreeing. i'm starting to get worried. >> reporter: micah shaheen was on the jury and said one holdout in particular was responsible for the stalemate. >> he started pounding on the door saying he wanted out of there. we were in tears, a lot of us, because we knew that we were up against a wall, that nothing else could be done with this person. >> after weeks of testimony and three full days of deliberations, the seth techel murder trial came to a sudden -- the judge declared a hung jury. punch to the gut? >> i never had one in 30 years. >> reporter: prosecutors immediately decided to retry the case. it had been 10-2 for conviction. >> of course we're disappointed. >> reporter: the caldwells had lost a daughter and sister, and now they couldn't even get the closure they desperately wanted. and they'd have to do it all over again. >> hard to know that you're going to have to endure another one. >> reporter: a trial date was set for seven months later, october, 2013, and trial number two would be heard in a new courthouse. there had been a change of venue to the town of mt. pleasant, making it even tougher on the caldwell the. the daily treks to court, lives disrupted. the new courtroom had a distinctive layout that put the caldwell family directly behind the defendant. >> he's literally sitting right in front of me. like you are. >> reporter: which only made it more frustrating for presley who was trying for any kind of connection to someone she once loved like a brother. >> i'm staring at him like glance at me, do something. he doesn't. >> reporter: and even more painful for the family was having to sit through again all that heartbreaking testimony and raw crime scene photos of their lisa and the unborn baby girl. other than the change of venue, seth techel's second murder trial played out as a carbon copy as the first. same lawyers, same judge, same arguments. a replay of two opposing theories. brian tate, the other suspect, versus seth techel, the husband with the other woman. rachel mcfarland was against the prosecution's star witness. >> here on may 4th of 2012, sent you a message with a picture of his own smiling face saying, "miss you, bella." was that a term of endearment that he called you? >> yes -- >> bella? >> yes. >> you sent him a picture of you in either a bikini or your bra and underwear, is that right? >> yes. >> and then he says, well, wish me luck. i love you. at 10:51 p.m. on may 24th of 2012. what was he asking you to wish him well with? >> i believe that he was going to tell her that he wanted a divorce. >> reporter: two days later, lisa was dead. by now, her family had hardened opinions about rachel. >> i don't think too highly of her. i felt like she destroyed my sister's marriage and her life. >> actually, i'm -- i'm maybe not the most popular view. i blame her for what part she had to play with seth, i mean i think she's kind of been a victim, as well. >> he's manic, up all the time. >> reporter: the defense offered the same boogieman as before. >> the defense went even harder at brian tate than they had the first time around. >> he could quickly become volatile and agitated. >> reporter: this time the defense over strenuous objections got seth's psychiatrist to testify. he treated him near the end of his life in a mental health unit. >> when you first saw him, did you find him paranoid, delusional? >> yes, sir. >> was there a general topic of delusion of which he was paranoid? >> he seemed to make reference that there were some governmental conspiracies affecting him. >> reporter: after three weeks of trial, a second jury had seth techel's fate in its hands. and that's when things got deja vu all over again. the judge read a note from the foreman. >> they are not going to reach a verdict. what's next? >> reporter: it's happening again. >> yeah. i'm thinking this is two months worth of trials and we're right back to the beginning. >> reporter: but the judge wasn't ready to give up. he told the jurors to keep trying. emotions in the open courtroom were raw, especially on the caldwell side. the jury couldn't help but hear it. >> presley and i were crying. we weren't crying uncontrollably or anything, but you could hear us sniffling a little. >> reporter: as the jury filed out, the defense attorney scolded the spectator, stop the over-the-top outbursts, or he would demand a mistrial in fairness to his client. >> i do not desire this jury to be influenced by the public. >> reporter: now it was the prosecutor's turn to seeth. >> the defense is making a speech about the caldwell family trying to small influence the jury which we thought was ludicrous. i squeezed andy's arm and said, "eye got this." to suggest that anyone is making an attempt to intentionally influence the jury is absolute nonsense. >> reporter: the courtroom started to settle down and clear. but seth remained at the defense table. his former father-in-law coiled behind him ready to pounce. >> i was praying, please just let me stand here. >> reporter: for more than a minute glaglaring, burning a ho in seth's back. if looks could kill. >> an urge to go forward. god, please don't let me do that. just let me stand. >> reporter: what were you doing in your mind? >> i don't want to think of what i was doing in my mind. i was wanting to do something. >> reporter: two hours later the jurors returned, but nothing had changed. >> mistrial is declared. >> reporter: unbelievable. veteran prosecutors who never had a hung jury before were now o-2. again the state didn't hesitate. seth techel would go on trial for a third time. >> our intent is to retry it. that was an easy decision to make. >> reporter: even though the jury's vote was again in favor of conviction, this time 9-3, lisa's family was starting to have its doubts. >> is there something i'm overlooking? did he not do it? is there something they see and they're like -- he's not guilty? >> reporter: but just when they thought they couldn't suffer anymore heartbreak, the caldwells would be devastated by new findings by a brand-new defense team. >> i heard it about a week before the trial. it was like somebody hit me in the stomach. >> reporter: coming up, the defense comes out swinging. >> we close to focus on the sloppy work done by the law enforcement. there was absolutely no dna, fingerprint, confession. ♪ ♪ the holidays are happening at lowe's. thank you! shop our winterfest event online now for pick up at the store. bye! ♪ and i'm gonna keep on lovin' you, ♪ ♪ 'cause it's the only thing i wanna do. ♪ turns out everyone does sound better in the shower. and it turns out the general is a quality insurance company that's been saving people money for nearly 60 years. ♪ 'cause it's the only thing i wanna do ♪ shaq: (singing in background) can't unhear that. for a great low rate, and nearly 60 years of quality coverage - make the right call and go with the general. it's another day. and nearly 60 years of quality coverage and anything could happen. it could be the day you welcome 1,200 guests and all their devices. or it could be the day there's a cyberthreat. only comcast business' secure network solutions give you the power of sd-wan and advanced security integrated on our activecore platform so you can control your network from anywhere, anytime. it's network management redefined. every day in business is a big day. we'll keep you ready for what's next. comcast business powering possibilities. two families, two trials, and so far no winners. but trial number three promised to be different starting with a new defense team. >> the previous trials were not successes, and seth came dangerously close to being convicted in each of them. >> reporter: state-appointed defense lawyers roger owens and jake firehelm knew that in two trials 19 of 24 jurors had voted to convict seth techel. they didn't like those numbers and decided to head in a different direction. >> we chose to focus on the sloppy work done by the law enforcement. there was absolutely no dna, fingerprint, confession. >> reporter: firehelm would argue it was a botched investigation. why would crime scene techs into test to match the slug to the murder weapon but never check it for fingerprint or that might link it to the shooter? did you test the bullet that was in the chamber that killed this woman? no. we forgot or didn't do it. >> reporter: oops. >> oops. >> reporter: the new defense team had a new story to tell. it was all a rush to judgment to blame seth who'd been in jail ever since his arrest two years earlier. and there was another big strategic shift. they would soften the focus on the boogieman of the first two trials, brian tate. >> our conclusion was after listening to the tapes of mr. tate, that he wasn't the deranged person that they tried to portray him as being. >> the way he was speaking to law enforcement that afternoon would not seem like the person that would have walked into a trailer home at 5:00 in the morning and murdered his neighbor. >> reporter: the defense attorneys made a tactical decision -- since recordings of tate didn't make him look like a dangerous killer, they would not show tapes of him to the jury, and they'd roll the dice hoping the prosecutors wouldn't either. the caldwells and techels had been put through the wringer for more than two years. their once close relationship had frayed, and now the third trial was pushing everyone to the brink. it was an impossible situation, but somehow todd caldwell and doug techel managed to find a moment of grace. >> i went over to him and just said, doug, i want you to know that i think you're a great guy. i think you're a good person. >> reporter: did you really? >> no matter how this turns out, i want you to know that. he said, "i think the same thing with you, todd," and i went to shake his hand and heap just hugged me, and we both just hugged. >> reporter: the two fathers returned to pot side of a murder -- opposite sides of a murder trial. for the third time the state of i what versus seth techel. >> are you ready for the jury? >> reporter: this time in davenport, three hours from the first courthouse in otumwa. the prosecutors once again argued that seth's story defied logic. >> he would have to be the victim of one of the largest coincidences ever known, and that is he told his girlfriend hoe left his wife and less than 17 hours later some unknown assailant breaks in and kills the wife that he says she's going to leave. >> reporter: with a weapon which he hasn't brought with him. >> direct. with a weapon he hasn't brought with him. >> a mosberg 1,200 shotgun. >> a 12 gauge? >> yes. >> reporter: and seth they said had easy access to the murder weapon, the shotgun that his friend lucas kept in his house. >> is that the mosberg shotgun that you left behind at the one went residence when you moved out in may of 2012? >> yes. >> reporter: and the prosecutors argued only seth had a motive. they said seth and rachel's steamy texts and photos played like hay countdown to murder by seth. >> on 294th you asked him do you really want to be with me, and he respond, "forever." >> right. yes. >> reporter: that's may 24th, two days before lisa's death. and in a followup text, rachel asks second if he told his wife he wanted a divorce yet. >> and he responded, "well, we talked, i told her i wasn't happy. she got mad, then sad, then i slept on the couch. so hello, mrs. resuscitator"? the. >> correct. >> reporter: the firefighter often bragged about his lifesaving cpr heroics. >> he was mr. reus istator and you were going to be mrs. resuscitator? >> yeah. >> reporter: to drive home the contention that seth chose murder over divorce, prosecutors called a co-worker who'd been a confidante of seth's. >> i expressed that he needed to either end his marriage or end it with rachel. >> and saying that he should end his marriage with lisa techel, did he make any comment concerning child support? >> he asked me if i wanted to pay his child support. >> reporter: then the witness recalled another remark seth made about lisa. >> he stated that it would be better off if she was in a car wreck and died. >> reporter: prosecutors hoped their third time would be the charm. but the new defense attorneys would come at them with everything they had. and that included explosive new evidence. this time it was about lisa. coming up -- you found out the story that there was this guy, co-worker? >> right. >> reporter: was there another man in lisa's life? why hide your skin if dupixent has your moderate-to-severe eczema, or atopic dermatitis under control? hide our skin? not us. because dupixent targets a root cause of eczema, it helps heal your skin from within, keeping you one step ahead of it. and for kids ages 6 and up, that means clearer skin, and noticeably less itch. hide my skin? not me. by helping to control eczema with dupixent, you can change how their skin looks and feels. and that's the kind of change you notice. hide my skin? 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>> i tried to be as straightforward as i could with the jury. who in the world is going to murder their wife to facilitate a relationship that hasn't even turned sexual? >> not having any sex with this man, right? >> correct. >> and the only time that you'd ever seen him in person in your whole entire life out the work was four or five times. >> correct. >> i have no further questions. we wanted the jury to think that you're going to shoot your wife for this. >> reporter: the attorneys then went on the attack, characterizing the work of investigators as woefully shoddy. >> inconsistent, incompetent, incomplete -- >> reporter: the new deficit thrust was on what investigators did not do. the state criminalist had to ad mist they did not test for gunshot residue on seth techel. >> how many times did you testify that gunshot residue was evidence of the crime? >> a lot. >> but in this case, we can't argue because we don't have it. >> yeah. exactly. we'll never know. >> never know. >> reporter: and the defense said it was even more shocking that the state expert had to make a similar admission about the fatal shotgun shell. >> this is the shell that killed lisa techel. >> yes. >> the very shell that killed this woman was never examined by the state. they just said we forgot to do it. >> reporter: but the centerpiece of the defense case against the cops was something else they didn't do. they'd been so busy investigating seth, who'd been behind bars since his arrest two years before, that they never really paid attention to lisa. the new defense team would change all that starting with her cell phone and the secrets it held. you found out the story told by the phone, that there was some guy, co-worker -- >> right. >> reporter: it was a bombshell. lisa was having an affair with a fellow jailer. her lover was a married man, a father of four. this is not making out in the back of the car. >> no. he thought he -- he could be the father of the child. he thought that. >> reporter: so they called lisa's lover, jason tennis, to the stand. and back in may of 2012, did you know a lisa techel? >> yes, i do. >> reporter: jason testified that the affair started before lisa married seth and ended just weeks before her murder. >> mr. tennis, at some point did your relationship with lisa techel become sexual? >> yes, it did. >> when we talk about a sexual relationship, we're not talking about texting. are we? >> no, sir. >> reporter: you're talking about actual sexual intercourse. >> yes, sir. >> reporter: for lisa's father, the revelation that his daughter had a lover was the cruelest blow yet. >> the first emotion i had was why, why, lisa, you know. and my second thought is, i don't want to tell amy because i know she's not going to be happy. >> reporter: does it taint your memory at all? >> really what it did for me more than anything is i have so many more questions that i'll never get the chance to ask her. i mean, i love lisa. and she was a human being. she made mistakes. >> reporter: the graphic testimony about lisa's affair and how police overlooked it fit perfectly with the defense's theme of a botched investigation and a rush to judgment against seth. >> here's a legitimate suspect that should have been investigated. >> reporter: investigators never spoke to jason while they were building their case against seth. prosecutors finally contacted him just days before the third trial started. >> between may of 2012 and sometime in june of 2014 no one talked to you -- didn't talk to anyone about this at all? >> no, sir. >> reporter: but prosecutors fought back. jason had an alibi witness -- his wife. they called her to the stand. >> do you have any memory, miss tennis, as to the whereabouts of your husband on may 26th, 2012, at approximately 5:00 a.m.? >> he was sleeping with me at our house. >> reporter: and dna testing on jason done right before trial also proved he was not the father of lisa's baby. but the defense still believed that raising the story of lisa's affair and how police never uncovered it would give jurors reasonable doubt about the entire investigation. this is a big part of your case in trial three, jurors, you're seeing some shabby police work here in terms of investigation. >> fell right into our theory of the case. >> reporter: testimony in the third trial streamlined by both sides took half the time the others did. that was another part of the new defense team's revised strategy. there had already been five holdout jurors in the previous two trials. now todd caldwell worried that the new team had produced a cloud of even more reasonable doubt. >> okay, if i was on this side, that's kind of how i would have handled it. they're doing a pretty good job. i'm con vinesed going to be -- convinced going to be another hung jury. why wouldn't it be? >> reporter: coming up, todd and just about everyone else are in for a surprise. >> has some jury reached a verdict? verdict? july 24th, 2014, after two agonizing stalemates, this time things were different. as seth techel walked into the courtroom and sat down, his face showed no expression, no hint of emotion. he didn't glance in any direction, not at his family, and certainly not at todd, his former father-in-law. >> this is the young guy used to clap on the back and say, "i love you." >> just take care of her, that's all i ask. >> reporter: todd was staring directly at seth hoping to find something, anything. now the moment was at hand. >> has this jury reached a verdict? >> it has. >> reporter: the judge asked the court attendant to read the verdict. lisa's mother could barely contain her emotions. lisa's sister a bundle of nerves. >> count one, we the jury find the defendant, seth andrew techel, guilty of murder in the first degree. psyched by the head -- signed by the head juror. count two, nonconsensual termination of human pregnancy, guilty of nonconsensual -- >> reporter: the justice system had finally spoken for lisa and unborn zoe. then you hear the words -- >> the words "guilty." i see nothing, not one single emotion from his face. >> reporter: the jurors had taken four hours to convict. on their way out, several reached across to shake tracy's hand. presley still had one big question -- >> i would love to ask him why. there's seth before me, 26, and then there's seth from may 26th on. it's almost like i don't know who that is. >> reporter: seth's parents tried to fight back tears. >> it was heartbreaking. >> reporter: on the caldwell side, tears of joy and displays of overwhelming relief. there were hugs and more hugs. more than two years of pent-up emotions finally coming out. the caldwells then walked across the aisle, the two moms embraced united in tragedy. >> we know this family. i know it's not doug and lorraine's fault. it's not their family's fault that any of this happened. >> reporter: todd searched out doug. only three years before they were all celebrating their kids' wedding together. doug and lorraine still support their son and say he didn't do what he's now convicted of doing. do you have a whisper of doubt, either of you? >> no, sirment none whatsoever. i never have, and i never will. everybody's a loser. nobody winds. i will say this -- i think lisa knows somewhere that the system that she wanted to be a part of worked. >> reporter: the caldwells and techels weren't the only ones with a stake in the verdict. brian tate's sister sherri had been waiting for this moment, too. >> i started crying. it wasn't tears of sorrow. it was tears of joy. they had finally gotten this s.o.b. i hope he rots in prison. >> reporter: todd still carries the burden of helping to pin the blame on tate in those awful moments after lisa's murder. >> i can never tell the family how sorry i am that they had to go through what they had to. we're going to have the last word on brian tate. this is an innocent guy that was made a victim by seth. >> all rise. >> reporter: a sentencing hearing was held in september, 2014. the caldwells were given a chance to address the court but talked directly to seth. >> you know how close lisa and i was, and you know what you took from me. out of everybody in this room, you know. >> reporter: presley, lisa's sister, walked up to take her turn. during all three trials, she desperately tried to make eye contact with seth. >> seth was my best friend, my brother, i loved so much. >> reporter: now she finally got what she wanted. as she spoke, she looked straight at him. for the first time, seth stared right back at her. >> i'm going to leave you with one final thought that i'm no longer your sister, and i no longer love you. >> reporter: then the judge handed down the sentence. life in prison with no possibility of parole. when it was finally all over, todd went to the cemetery for a private moment with his oldest daughter. >> i went out there, and i told her that we did it. she could be proud of everybody. >> reporter: todd's been back many times since. lisa's grave is a special deeply personal place for him. he designed her headstone. what do the figures in it? >> the first thing i would do when i started sketching it is i would draw a heart out. for some reason in my head it should be in the shape a heart. second thing i would put is a mother holding a baby, andleasea and i had -- and lisa and i had this thing we would say. we texted each other and everything, it's from "the notebook," movie. we always said, if you're a bird, i'm a bird. meaning -- whatever you are, i am. so in the era of this i made two birds in there. by the time i got it done with, we all loved it, and it was kind of bonded like, hey, this is part of lisa now. i'm craig melvin. >> and i'm natalie morales. >> and this is "dateline." she was very carefree, loving. she was amazing. i just can't tell you the feeling that went through my mind. i couldn't think of anybody that would ever want to do what they did to her. >> amyjane was an angel. traveling the world with her church to help children. >> they loved amy. they loved amy so much. >> but back home something sinister lay waiting. >> it was a pretty horrific crime scene. >> a bright young