lunch. >> where was she? >> there were just no answers. >> reporter: nearly 30 years, 670 investigators. and it just kept coming back to one. >> he just very calmly said, "i know how to get rid of a body so it would never, ever be found.” >> we were just a heartbeat away from losing a witness, to not having a case. it was basically a now-or-never situation. >> reporter: welcome to "dateline." when kathy heckel disappeared, police didn't know if they were dealing with a missing person's case or cold blooded murder. and the investigation grew cold. decades later, a young detective who was just a kid when kathy vanished dusted off the old files. investigators couldn't solve her case then. could he help solve it now? here is josh with "she didn't come home." >> reporter: time can be like a river. a long stream of events rushing by. most barely make a ripple. but a few, like the sudden loss of a close friend, a child, or a parent, have a way of circling back upon us in a ceaseless loop of memory and regret. that's the way it's been for john heckel and his sister alicia talbot ever since that completely normal morning in 1991 when their mom, kathy heckel, kissed them goodbye, left for work and never returned. >> you remember her leaving that morning? >> yeah. i -- i mean like every other day. >> yeah. >> same routine all the time, every time she left us, she kissed us goodbye. >> reporter: it was a july morning. alicia, 13, and john, then nine, were home for summer vacation. a little after 9:00 a.m., alicia says her mom called from her job. >> we discussed having dinner and having pork chops. >> uh-huh. yeah. 'cause that was one of my favorite things she cooked. >> reporter: later, they tried to contact their mom at work. >> one of the times we tried to call her was around lunchtime. and she had left for lunch. >> yeah. >> and then we waited and called after lunch, and she still wasn't back to work yet. >> reporter: at 40, kathy heckel had spent half her life working at the local paper plant in lock haven, pennsylvania. >> i can't remember who i was speaking to at the office. but you could hear in their voice that there was some concern there that she hadn't come back yet. >> and you picked that up. >> yeah. it was not typical for her to not come back and not tell anybody. >> reporter: with their dad out of town, they kept trying to reach their mom. nothing. at about 6:30 that evening, alicia called her grandparents, clarence and margaret dolan. >> i answered the phone. it was alicia. she said, "gram, can you get us some milk?” and i said, "what -- what do you mean, can i get ya some milk?” she says, "well, mom didn't come home yet," and she says, "we don't have any milk. and i said, "alicia, i will be right there.” >> and you're thinking what? >> i didn't know what to think. but as a mother, you know that this is something bad, something very bad. >> reporter: that night, kathy's mother and father contacted everyone they could think of. >> no one had heard from her. and that was -- i remember picking up on that, that they seemed -- they seemed worried. >> i mean you could just tell. >> your grandparents were acting differently? >> uh-huh. >> uh-huh. >> reporter: their dad, john, was in upstate new york that monday training with his national guard unit. he didn't learn his wife was missing until the next day. >> you get that phone call. it's your mom. >> yeah. >> what'd she say? >> the gist of the conversation was that kathy didn't come home from work on monday night. and they didn't know where she was. >> and now it's tuesday. >> and now it's tuesday evening. >> and you think what? >> i said, "time to call the state police.” >> reporter: with the permission of his commanding officer, john heckel immediately left for home. he had plenty of time to think on that five and half hour ride. he thought about the time kathy donated a kidney to save her brother's life and about the december day in 1972 when he first gazed at kathy dolan. >> she just had the biggest brown eyes you could look into. >> reporter: six months later, they were married. >> like any marriage, i think we had our ups and downs. but overall, i was happy about the fact i didn't have to worry about my family with kathy. >> you thought you were gonna stay married forever? >> yes. >> reporter: the problem was, john was already married to the military. john's career frequently took him away from home. sometimes for weeks at a time. kathy didn't like that. and john says his wife of 18 years seemed to have that on her mind when she'd dropped him off for his latest guard assignment. >> she asked me why i had to be there so early, which didn't make sense to me because i was always the first one there. and i said, "it's my job.” >> she didn't want you to go? >> she didn't say "i don't want you to go.” >> but you felt it. >> i could feel that something was wrong. the look on her face when she said it, it's -- it just didn't set right with me. >> reporter: now kathy was missing and her disappearance would eventually drag into the open secrets that some in and around lock haven would have rather kept hidden. >> reporter: no doubt kathy took good care of her family. but as investigators soon learned, this was also a woman who was sometimes lonely. coming up -- >> i asked her moem if sheflsz seeing anyone. and she said that she had re-established contact with an old friend from school. >> and that old friend had a confession to make. >> he did admit that they had had a physical relationship. and it had only been a few days before she disappeared. when eye allergens attack, the itch can last 24 hours. but with pataday once daily relief extra strength you get fast, 24-hour relief in one drop. make it a pataday with the drop that's right for you. now without a prescription. everywhere. nexgard is the flea and tick protection that's #1 with vets. it even prevents the infection that causes lyme disease. your vet trusts nexgard for her patients and her own dog. plus, its delicious beef flavor is #1 with dogs. ask your vet about nexgard. these are real people, not actors, who've got their eczema under control. with less eczema, you can show more skin. so roll up those sleeves. and help heal your skin from within with dupixent. dupixent is the first treatment of its kind that continuously treats moderate-to-severe eczema, or atopic dermatitis, even between flare ups. dupixent is a biologic, and not a cream or steroid. many people taking dupixent saw clear or almost clear skin, and, had significantly less itch. don't use if you're allergic to dupixent. serious allergic reactions can occur, including anaphylaxis, which is severe. tell your doctor about new or worsening eye problems, such as eye pain or vision changes, or a parasitic infection. if you take asthma medicines, don't change or stop them without talking to your doctor. so help heal your skin from within, and talk to your eczema specialist about dupixent. if your financial situation has changed, we may be able to help. alright, guys, no insurance talk on beach day. -i'm down. -yes, please. [ chuckles ] don't get me wrong, i love my rv, but insuring it is such a hassle. same with my boat. the insurance bills are through the roof. -[ sighs ] -be cool. i wish i could group my insurance stuff. -[ coughs ] bundle. -the house, the car, the rv. like a cluster. an insurance cluster. -woosah. -[ chuckles ] -i doubt that exists. -it's a bundle! it's a bundle, and it saves you money! hi. i'm flo from progressive, and i couldn't help but overhear... super fun beach day, everybody. >> reporter: by the time john heckel returned home from national guard training in new york state, his wife kathy had been missing for about 36 hours. >> when my dad came back, he was the one who told us, "we can't find your mom. we don't know where your mom is.” and that was the first time i've ever seen my dad cry. and i -- i knew the worst had definitely happened if he was that worried. >> and that was the first time i saw my dad cry, too. and, you know, he was always this big, strong man. and -- and when you see that, is -- this is not good.” >> reporter: that's gotta be a terrible thing to tell your kids. 'cause they want -- they want you to tell them, "this is gonna be okay.” >> dad always had all the answers. >> and you can't tell them this is gonna be okay. >> no. you don't want fabrication. >> reporter: across town that morning, pennsylvania state trooper fred caldwell was on the case. his first call had been to margaret dolan, kathy's mom. >> i remember asking her if she had noticed any changes recently or anything in her demeanor that was unusual. and she said that in the last four to six weeks or so, she just wasn't herself. >> reporter: then the trooper asked one of those probing, indelicate questions that cops have to ask. >> i asked her mom if she had any indication that she was seeing anyone. and she said that she had reestablished contact with an old acquaintance, an old friend from school. >> that man's name was dennis taylor. he and kathy had recently reconnected at a wedding. taylor had been singing and playing guitar. the trooper jotted down the name dennis taylor with the idea of calling him later. next he dialed the paper plant where kathy was last seen. one of kathy's co-workers picked up the phone. >> she kinda corroborated what her mom had said, that she'd been a little different in the last few weeks, personality just seemed a little quieter maybe. >> reporter: then he asked question number two. >> i also asked her if she felt that there was a possibility that she may have been having an affair or seeing anyone. and she said she had no evidence but she suspected that she may have been. >> the co-worker wasn't talking about kathy's friend, dennis taylor. she was talking about a man at the plant named loyd groves. >> they both played on the same volleyball team. they spent some time after hours together. and i think just the closeness of the two and she just kinda suspected that they may be. >> reporter: the trooper learned groves was the quiet type. married with children. sometimes he led plant tours and gave paper-making presentations to local schools. a call to groves' office revealed he wasn't in yet. so the trooper left a call back message. and not long after, the trooper says mr. groves showed up in person at the state police barracks. >> he was very calm. he said that he knew her. they share -- they worked in the same office areas. he said they were friends. i did ask him if he had any type of physical relationship with her and he said no. >> reporter: shortly after loyd groves left the state police barracks, the other man on trooper caldwell's list walked in. dennis taylor, the guitar man. like groves, taylor was married man with children. and right off the bat, he told the trooper he had a confession to make. >> he did admit that they had had a physical relationship briefly. and it had only been a few days before she disappeared, as i recall, the first contact, physical contact. >> reporter: like a balladeer who knows his audience is hanging on every lyric, the guitar man kept singing to the cops. taylor told the trooper kathy heckel had called him at work the day she disappeared. her voice, he said, had a strange tone. >> she called him just before lunchtime and was upset or anxious and said that she had something she wanted to talk to him about. and he was busy. and he said, "i can't talk. i'll call you back," and hung up. he did try to call back then sometime later. and she had gone for lunch. >> reporter: taylor said he'd played golf with friends that afternoon and had planned to meet up with kathy later that night. >> denny goes to their location where they're gonna meet. kathy doesn't show up. he was concerned that something may have happened. >> reporter: it was then the guitar man struck a familiar chord. kathy heckel, he said, had also been seeing another man. a guy named loyd groves. according to taylor, this fellow groves was a bit of a stalker. >> he said that he had met kathy at a park, a nearby park. he said that there was a gray van parked nearby. he recalled seeing the van. and the next time he talked to kathy she said, "did you see that van? that was loyd.” and he was following her. >> reporter: was the guitar man being helpful, or was he trying to implicate a rival to save his own skin? the trooper knew this much. if kathy heckel had been juggling simultaneous affairs with married men, there could be a lot of people who wanted her to disappear including her husband. >> he was definitely a person of interest. >> reporter: exactly how much did john heckel know about what was going on in his wife's life? could go -- could go - were police looking for a runaway wife or her killer? >> there were just no answers. and that was -- that was the worst part. >> reporter: did you feel like you were ever a suspect? >> never worried about it, i knew they were trying to find where kathy was and what had happened. if that included questioning me, i had no problems with that. so you're a small business, or a big one. you were thriving, but then... oh. ah. okay. plan, pivot. how do you bounce back? you don't, you bounce forward, with serious and reliable internet. powered by the largest gig speed network in america. but is it secure? sure it's secure. and even if the power goes down, your connection doesn't. so how do i do this? you don't do this. we do this, together. bounce forward, with comcast business. >> reporter: any investigation in which someone goes missing or turns up dead -- just about guarantees family members will be considered suspects. kathy heckel's husband john was no exception. >> we did consider that john may have known that his wife was having an affair and that he may have taken some action on his own. >> did you feel like you were ever a suspect? >> never worried about it. i knew they were tryin' to find where kathy was and what had happened. and if that included questioning me, i have no problems with that. >> at some point somebody said to you, "we believe she was having a relationship with some other people.” was that shocking to hear? >> it was surprising, because that wasn't the way kathy was. >> reporter: in his interview with trooper caldwell, john heckel said he'd noticed a change in his wife's demeanor in recent weeks and wondered if she might be having an affair. >> he was emotional. there's times when john and i just sat together with my arm around him and he would cry. he was concerned about his wife. and i felt very bad for the man. >> reporter: john heckel's alibi checked out. and police found no evidence he'd paid anyone to hurt his wife. by now, kathy had been missing for two full days and john heckel feared the worst. >> kathy heckel would never on this earth abandon those two children. >> reporter: trooper caldwell still didn't know if he was working a missing persons case, an abduction or a homicide. then on the evening of the third day investigators got a big break. they found kathy heckel's car parked behind the local hospital. the keys were missing. >> i think they recovered one print. but i don't know that it was ever identified. it was from the exterior of the car. >> reporter: investigators were now pretty sure that someone, possibly her killer, had moved kathy heckel's car to the hospital parking lot. and then the case hit a dead end. days turned to weeks. those weeks stretched into months. kathy heckel was somewhere in the wind. >> we had cadaver dogs come down often. and we would have troopers go out and we would search the area looking for remains or whatever. >> reporter: while some investigators focused on finding kathy heckel, others concentrated on finding evidence of a crime. as far as investigators could tell, the guitar man, dennis taylor, had been honest, confessing his affair with kathy heckel. loyd groves, on the other hand, had seemed a bit dodgy. troopers had searched loyd groves home, office and van. and while some items of interest were found, the local prosecutor didn't think police had enough to make an arrest. >> there was a big hole from an investigative standpoint. >> reporter: ted mcknight was clinton county district attorney at the time. >> if you can imagine a yardstick, and probable cause is probably at the two inch mark, and beyond a reasonable doubt is probably at the 34 inch mark. and everything else in between is the difference between are you gonna get a conviction or aren't ya. >> which means you don't go forward unless you're reasonably sure you have the evidence for a conviction. >> correct. >> reporter: he says the fact that kathy heckel's body had not been found was a big problem. >> how do we prove beyond a reasonable doubt that she is dead? if she was killed, where did the killing occur? what county did it occur in? >> maybe it's not even your jurisdiction? >> correct. >> reporter: for the heckel family, kathy's disappearance was a defining event. >> i remember being depressed. i didn't know what that meant when i was nine years old. but just thinking about how low and sad i felt all of the time. >> i think people deal with things differently. and i certainly chose, i think, the avoidance method. >> not think about it. >> and not think about it. >> there were just no answers. and that was -- that was the worst part. >> reporter: in 1998, seven years after kathy disappeared, john heckel had his wife declared legally dead. that did not make the mystery any easier for him to understand. >> can you accept the idea that, maybe, there were needs that she felt that she had to meet with men who were not you? but that she still loved you. >> oh, no. i believe she did love me. >> she had a secret life that she wasn't showin' anybody else. >> but you don't know how long that secret life was, and neither do i. it could have been her plan to wanna end that the day when she asked me why i had to leave so early. i don't know. but i'm not gonna hate her for being human. >> do you blame yourself? >> little bit. >> reporter: 22 summers came and went. john heckel remarried. the kids grew up. they started new lives out west. alicia became a ski pro, john, a fishing guide. but through it all, their mother was never far from their thoughts. >> she missed all those childhood memories. i mean things like going to the prom, and boyfriends, and kisses and just -- just everything. >> yeah, she missed our weddings. i mean she missed our graduations. she doesn't know her only grandchild. >> and you probably thought about her at each one of those. >> mm-hmm. >> mm-hmm. >> reporter: clinton county never forgot kathy heckel either. she'd become a part of history that just wouldn't go away. and as one generation of lawmen retired, another rose to take up the unfinished business and discovered enticing details buried in a very old file. coming up -- >> when i obtained this case it was 22 years old. >> had passed through a lot of other hands. >> he was eight years old when kathy disappeared. now he was in charge of her case. >> what i remember growing up is, where was she? where was kathy at during all this time? >> and a leading suspect suddenly leaves town. >> about three weeks after the disappearance of kathy, he moved his family back to beaver, pa. ♪ ♪ the chevy silverado trail boss. when you have a two-inch lift. when you have goodyear duratrac tires. when you have rancho shocks and an integrated dual exhaust. when you have all that, the last thing you'll need... is a road. the chevy silverado trail boss. ready to off-road, right from the factory. feel the cool rush of claritin cool mint chewables. powerful 24-hour, non-drowsy, allergy relief plus an immediate cooling sensation for your throat. feel the clarity, and live claritin clear. why choose proven quality sleep from sleep number? because a good night's rest is where muscles recover, and our minds are restored. introducing the new sleep number 360 smart bed. the only bed that effortlessly adjusts to both of you. proven quality sleep, is life-changing sleep. here is what is happening. the san diego convention center emergency intake site is receiving it's first 500 unaccompanied migrant children. hhs says that it will provide shelter to 13 to 17-year-old girls. it has the potential capacity for 1400 beds. and cities around the world turn their lights off to mark earth hour. australia sydney harbor bridge and sky tower are among the landmarks that went dark. the movement focuses on sustainability and climate change. now back to dit line oig. . welcome back. investigators suspected that kathy heckel may have been murdered. but with no body and little evidence, the case went into a deep freeze for decades. kathy's family had never been able to shake the chill of their inconceivable loss. but now a new detective is about to turn until here. here again is she didn't come home. >> reporter: for more than 20 years, kathy heckel's children lived with a feeling of unfocused fear. >> it's an unsettling feeling that -- an unsettling feeling of fear that essentially something great in my life can be taken away at any moment. >> and you think that can all be traced back to your mom? >> absolutely. >> absolutely. >> reporter: for their father john, those were years spent struggling to let go and move on. >> i talked to kathy a lot about it. >> what do you say to her? >> just talk, just ramble on. >> and you just start talking to her out loud? >> yeah. something'll come up that'll remind me of something we did. >> reporter: law enforcement had not forgotten kathy heckel. in the summer of 2013, a native son inherited the case, state police investigator curtis confer. >> when i obtained this case, it was 22 years old. >> and it had passed through a lot of other hands. >> 60 other investigators. >> 60? >> 60. >> and you thought i'm gonna close it or be the 61st and in a lyle while there will be a 62nd. >> well, josh, what was interesting was it was 400 pages of reports, and i just read it. >> reporter: to this 61st investigator, the reports were riveting. he'd heard the story as a child, and even had a connection to loyd groves, whose name was all over that file. >> he came to my elementary school and did a presentation on making paper. >> you saw a photo of him giving these -- >> yeah. and i went, you know what? i remember him doing our school. >> reporter: confer was now convinced that at the time this picture was taken, loyd groves was having an affair with kathy heckel. only two months later, investigators considered groves a suspect in her disappearance. >> what i remember growing up is where was she? where was kathy at during all of this time? john heckel was my brother's soccer coach. >> reporter: the case files were chock full of details. a gun found in loyd groves desk drawer. ammo found in his van. a curious chunk of carpet missing from the back of the van. >> what was loyd's explanation for cutting the carpet out of the van? >> in 1991, he said that the kids were playing with tar and oil and they got tar and oil in that section of the van. >> that confirmed by anybody? >> no, it was not. >> reporter: that wasn't the only thing to jump off the page. the original investigators had a witness who'd reported seeing investigators found was that loyd groves wrote a letter to h disappearance? >> this is right after the disappearance, and he wrote detailed notes to his wife on how to take care of the tractor, how to take care of the car. >> this is a guy who likes to plan. >> he is a planner, yes, meticulous. >> but he's not arrested. he was wrong. >> yeah, he was not arrested. about three weeks after the disappearance of kathy, he moved his family back to beaver, pa, and then eventually selling his home, leaving -- leaving a lot of his personal items at his home. >> reporter: when he finished reading the case file, confer called the local fbi office looking for some items connected to the case. it was then that he connected with mike hutson, a veteran state trooper assigned to a joint terrorism task force. after confer explained what he was after, hutson asked to see the file. >> i thought it was a very good case. i felt that there was, you know, a very real suspect. >> reporter: when hutson's partner, fbi agent and former prosecutor kyle moore read the file, he too was hooked. >> this is something we wanted to do something about. we wanted to see if there was any way that, you know, we could actually bring it to a conclusion. >> reporter: so within days of getting the case, investigator number 61 had a team to help him. >> they had so much knowledge that i didn't have, it was by the grace of god that they helped me with this case. >> reporter: time, it became clear, was not on their side. >> it was basically a now-or-never situation, and i always felt we were just a heartbeat away from losing a witness, to not having a case. >> reporter: as they worked the case the investigators knew they had one ace in the hole. in 1991, specks of blood had been found in loyd groves' van. advanced dna tests were done in 2004. >> based off the fact that there wasn't a dna sample from the victim, they essentially had to construct one from the victim's mother and father, essentially building the victim's dna profile. >> reporter: that dna test proved the blood was kathy heckel's, but trooper confer says it seems that bit of evidence fell through the cracks because the lead investigator and primary prosecutor at the time took medical leave. one thing was clear to all three of the new investigators, this case needed more resources and more prosecutorial muscle than clinton county possessed. >> we requested that the district attorney relinquish the case to the attorney general's office, and the d.a. at the time agreed. >> reporter: in early 2014 a grand jury was empaneled to review the evidence. hutson, moore and confer hit the road. >> so we did interviews in different states, and traveled the country a little bit. >> reporter: the new investigators tracked down old witnesses and even found a new one. a man who remembered an argument between kathy heckel and loyd groves on the day she went missing. the question was did police have enough to make an arrest? coming up -- >> i got to know this family. i was worried a lot about them because i knew this would be an ugly trial. >> reporter: will it be kathy who ends up on trial? >> every single indiscretion of hers would be announced in open court. >> she was going to be punished for being murdered. ♪ ♪i've got the brains you've got the looks♪ ♪let's make lots of money♪ ♪you've got the brawn♪ ♪i've got the brains♪ ♪let's make lots of♪ ♪uh uh uh♪ ♪oohhh there's a lot of opportunities♪ with allstate, drivers who switched saved over $700. saving is easy when you're in good hands. allstate click or call to switch today. these are real people, not actors, who've got their eczema under control. with less eczema, you can show more skin. so roll up those sleeves. and help heal your skin from within with dupixent. dupixent is the first treatment of its kind that continuously treats moderate-to-severe eczema, or atopic dermatitis, even between flare ups. dupixent is a biologic, and not a cream or steroid. many people taking dupixent saw clear or almost clear skin, and, had significantly less itch. don't use if you're allergic to dupixent. serious allergic reactions can occur, including anaphylaxis, which is severe. tell your doctor about new or worsening eye problems, such as eye pain or vision changes, or a parasitic infection. if you take asthma medicines, don't change or stop them without talking to your doctor. so help heal your skin from within, and talk to your eczema specialist about dupixent. if your financial situation has changed, we may be able to help. mom: look at you. no braces, if your financial situation has changed, all the internet you can handle. i wasn't so lucky. vo: invis is not your parent's braces vo: invis is predictable... less painful, more comfortable. invisalign. ♪ ♪ it's like a flavor festival on an almond. zest fest. -zest fest. blue diamond almonds, super flavor all on a superfood. the #1 name in flea and tick protection frontline® plus kills fleas, ticks, and chewing lice, and its fast-acting, waterproof formula protects for a full 30 days. with frontline plus, and new frontline shield for dogs with tick and mosquito repellency... you and your pet can go everywhere. ♪♪ ♪♪ no matter how you define it. frontline®. here. there. everywhere. ♪♪ - [announcer] we're thrive cosmetics, we create high performance, cruelty free, 100% vegan formulas and we love that you love our products. like our award winning liquid lash extensions mascara. plus, with every product you purchase we donate to help a woman thrive. join our movement today at thrivecosmetics.com. >> reporter: as a military man, john heckel finds solace on old battlefields. the past is always present there. but for john, no peace could be found here as long as his wife's killer walked free. >> i would always say, "where are we? how close are we to getting him arrested?" >> and police would say, "the d.a. won't go forward.” >> yeah, no. it -- it's more like, "we need more.” >> the investigators went looking for more. they tracked down new witnesses and dug deep looking for kathy heckel's body. which they never found. even so, on january 28, 2015, a grand jury indicted loyd groves for murder, largely on the strength of the same evidence that had been in the files all along. >> it was literally just like television. we got there early, at like 5:00, and we set up. as he was walking to his car, we rolled right up, jumped out. and when i put the handcuffs on him, i said, "you're under the arrest for the murder of kathy heckel.” >> did he say anything? >> yeah, he told his son that he needed to get a different ride to work. >> so -- >> it really didn't faze him. >> reporter: lo and behold, loyd groves is arrested. what was that like to hear? >> inner-thankfulness that we were getting somewhere. >> still a long way to go. >> yeah. still a long way to go. >> reporter: in many ways, the arrest of 65-year-old loyd groves was the easy part. legal maneuvering delayed his trial another three and a half years. for the defense, the delay gave their investigators time to poke holes in the prosecution's case. >> this case had holes you could drive trucks through. >> reporter: tom bruno and his wife, amy, were the defense team's investigators. >> we were in the case for nearly four years. we actually talked about him, i would guarantee every day. >> reporter: tom, a former cop, knew how to look for flaws in the police work. amy, a lock haven native, had grown up with the kathy heckel story. >> you talk to anyone in town, they would all say that loyd killed her and he put her in a vat of acid and dissolved her body. that was the working theory for years. >> reporter: but tom says the files he read didn't prove any of that. in fact, he says he found a silver bullet in those piles of documents. >> we actually discovered that in the police reports, in medical records, that she had cut her finger at work. it was bleeding so badly that she had to get it treated three times. and this was at the time that she was allegedly in her -- in loyd's van every day. >> reporter: so if the prosecution planned to make a big deal out of a dna test showing kathy heckel's blood in loyd groves' van, the defense response now would be so what. >> they think it came from kathy because loyd killed her. but yet, here's kathy's blood because she cut herself at work. >> i mean, if this isn't reasonable doubt, what is? >> reporter: as the case went to trial in november, 2018, pennsylvania senior deputy attorney general daniel dye knew the defense would do more than just attack their evidence. he feared they would attack kathy heckel too. >> i got to know this family. i worried a lot about them because i knew this would be an ugly trial. >> and that every single indiscretion of hers was going to be announced in open court? >> she was going to be punished for being murdered. >> reporter: the prosecution's case, almost entirely circumstantial, began with testimony from kathy heckel's children. >> it was a little difficult. but it felt good to be in front of loyd groves and have him look at me and listen to my story. >> and how scary it was? >> uh-huh. >> uh-huh. >> reporter: according to friends and family, kathy heckel was a devoted daughter, a loving mom. at the same time, she was also restless. >> tell me what was going on in her life at that time? >> her life at that time was a lonely life. john heckel is a good guy. but his first love was the military. and kathy was, you know, having affairs and one of them was with loyd groves. >> reporter: another lover, the guitar man, dennis taylor, said kathy had told him all about that unraveling affair. >> kathy was trying to break off the relationship. we know that. loyd did not want the relationship to end. and he specifically wanted to meet for lunch on that day. >> did loyd groves know about denny taylor? >> he did. we had evidence in the case that groves was following kathy. >> taylor testified that kathy had expressed some fear about loyd? >> right. >> in a special hearing, two former paper plant employees who'd been in poor health had their trial testimony prerecorded. one said he'd overheard kathy heckel and loyd groves arguing the day kathy went missing. >> just loud. >> reporter: the other said she saw loyd groves staring daggers at kathy heckel as she left for lunch that day. >> his face was so red, just like he was terribly angry. he was looking at kathy. >> kathy pulls out. loyd pulls out after. we believe that they did meet. that somehow, some way, kathy was cajoled into one last meet just to hear loyd out. and at that point in time, loyd shot her, shoved her in that van, likely with a head wound. >> reporter: according to witnesses, groves was back at the plant sometime between 2:00 and 3:00 that afternoon. >> you think loyd groves kills her, disposes of her body, and manages to get back to work that day and act like nothing's wrong and get away with it? >> i think it's because he's smart and a good planner. to him, i think, murder is something that can be done over a lunch hour. >> reporter: the prosecution wrapped up its case with two witnesses, people who only surfaced shortly before trial. the first was loyd groves' now ex-wife. >> there was something she had been holding back on telling for the past roughly 30 years. and that was that loyd groves did come home over the work hour on july 15th, 1991. >> something he almost never did? >> which he never did and changed out of his clothes. and she never saw the condition that those clothes were in. >> reporter: the next person to testify was this woman, gayle taylor. she also had a story to tell that she'd kept to herself for decades. it was the mid-'90s. taylor said that she and groves worked together in ohio. according to taylor, she went to groves one day to vent after she'd discovered drugs in her son's room. >> i was like, "i don't know what i'm gonna do with this kid. he's gonna get into trouble. he's gonna end up dying. if he -- if -- if the drugs don't kill him, his mother will.” and loyd was sitting at his desk and he just very calmly said, "well, i know how to get rid of a body so it would never, ever be found.” >> the defense's argument was he was joking? >> i sure wouldn't joke about being able to dispose of a body where no one could ever find it, if i had been investigated for killing somebody and they had never found the body. >> reporter: the prosecution closed its case by asking who but loyd groves could have killed kathy heckel? and in return, the defense stood ready to ask a provocative question of its own. could kathy heckel have simply run away? coming up -- >> did you really think she lived past that day? >> i certainly have a reasonable doubt as to whether she died that day. >> would the jury have the same doubt? >> it was a nervous moment, absolutely. 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>> reporter: and, of course, the defense argued, kathy's affairs could have also provided her husband with a motive for murder. weeks after kathy disappeared, the defense noted, john heckel discarded some of her personal items. >> her husband throws away her purse, her wallet, her -- her photo i.d. it isn't that he throws it in a garbage can in front of his house where someone might see it. it's in a dumpster in the back of a reserve base. >> you are saying he wanted to conceal that? >> what more logical conclusion is there? >> reporter: the defense didn't offer an answer for that and john heckel says he doesn't remember much about those days. the defense even suggested that kathy may not have died on july 15th, 1991. did you really think she lived past that day? >> i, certainly, have a reasonable doubt, as to whether she died that day. >> reporter: to support that theory, the defense introduced statements john heckel made more than 20 years ago. in one, he said he thought his wife may have syphoned thousands of dollars from a joint-bank account. in another, he asked investigators if a woman, pictured in a "swingers magazine" might be his wife. >> is there any, credible argument that kathy heckel squirrelled away money, vanished, ran out on her husband and her family, and then posed for pictures that were put in a swingers magazine, that anybody could have seen? >> i certainly don't think it has been disproven, beyond a reasonable doubt, that that could have occurred. >> reporter: on the stand, he said those decades-old statements had been the frantic musings of a desperate man. the defense conceded. groves did go home, that day, to change his shirt. but, said that was because he had gotten dirty, at the plant, where he had to lead a tour for a group of children at 3:00, that afternoon. and that lunch-hour trip home, they argued, simply made the prosecution's version events even more unlikely. >> if you factored in, all of the witnesses, when they saw him at the plant. how does he have anywhere-near enough time for him to have done what they claim he did some. >> reporter: for 27 years, the question of what had happened to kathy heckel had hung over lock haven. now, it was up to a clinton county jury to, finally, provide an answer. >> itself contentious. >> reporter: sean sanford, a toddler at the time kathy heckel disappeared, was the jury foreman. >> the very first vote we took was 7-5, 8-4, for guilty. i thought it was going to be the other way for acquittal. >> reporter: why did you vote for acquittal in that first vote? >> if you looked at every piece of evidence, individually, you could poke holes in all of it, piece by piece. >> reporter: after breaking for the weekend, the jury returned on monday morning. recollected but still deadlocked. >> there was one juror, in particular, who was voting for acquittal, originally, who couldn't get over the fact that he thought the prime suspect should be john heckel. >> over and over, jurors review squus the evidence. then, just before 3:00 that afternoon, jurors notified the judge they had reached a verdict. >> it -- it was a nervous moment, absolutely. i -- i was nervous. and we were all holding hands. >> reporter: on the charge of first degree or premeditated murder, the verdict was not guilty. then, in what seemed to be a compromise decision, the jury found groves guilty of third-degree murder. which is legally considered a spontaneous act, in the heat of the moment. you look at groves, during that time? >> no, i -- i spent more time looking at kathy's picture and crying. >> reporter: in a letter to "dateline," lloyd groves, once again, denied ever having had an affair with kathy heckel, and said he had been wrongly convicted. at the age of 69, groves was formally sentenced to serve 10-to-20 years in prison. >> even with the third-degree sentencing, he'll still spend the rest of his life in prison. >> that's enough for you? >> uh-huh. >> uh-huh. >> reporter: it's been more than a quarter century since the summer morning, when kathy heckel kissed her children good-bye. and although their wait for justice is finally over, they're still no closer to knowing where their mother is than they were on that summer night, in 1991 when she didn't come home. so, unless your mom's remains are found accidentally, you might not ever know. you going to be okay with that? >> we have to live with it. i mean, it's sad, and it's disappointing that we will never know. or we may never know. but we have to be okay with it. >> that's all for this edition of "dateline." i'm natalie morales. thank you for watching. i'm craig melvin. >> i'm natalie morales. >> and this is "dateline." anytime a child goes missing, it's a scary thing. you know there is evil out there. >> reporter: first, michella. >> it was terrifying. >> reporter: then, jenni. >> bloodhounds came. police were there. >> this is a little girl that was doing nothing more than riding her bicycle in a park. >> reporter: two young girls taken. >> the similarities. blonde, blue-eyed, riding a bike. >> somebody who is targeting young girls. >> exact