>> absolutely not. >> reporter: for the first time investigator defends his interrogation, which led to a conviction overturned. >> this was seen by many as a false confession. >> it was a real confession. >> we just need you to be honest with us. >> he knew right from wrong. >> those officers wanted that information in the worst way, and they got it in the worst way. >> reporter: the prosecutor fights back with an explosive new book. >> people are going to hear the other side of the story >> reporter: and a promise from steven avery's high-powered new attorney. >> do you think you have new evidence that can free steven avery? >> we do. >> reporter: i'm lester holt and this is "dateline." here's andrea canning with "return to manitowoc county." >> reporter: the mystery of what happened here in the sprawling fields of rural wisconsin has captivated the country. >> we the jury find the defendant steven a. avery guilty. >> reporter: just over a year ago, the netflix series 'making a murderer' convinced many viewers that steven avery and brendan dassey, both convicted of murder, had been railroaded by law enforcement. >> free steven avery! >> reporter: it's a case dateline has been following for more than a decade. >> reporter: tonight we bring you the latest in the efforts to free them from prison, and we pose the questions everyone's been asking to two men who helped put avery and dassey behind bars. >> why would steven avery do this ? >> that's a great question. >> reporter: we speak with former prosecutor ken kratz, who's written a new book which reveals his provocative theory. that steven avery made himself a murderer. >> steven avery started planning this event the very first day he went to prison >> reporter: and we talk with tom fassbender, a lead investigator who has come under fire for this controversial interrogation. now he's defending himself for the first time on television. why are you sitting here today? >> finally realized that someone needed to speak out, to bring forward the truth of what happened. >> so, what did happen here? >> reporter: our story begins with the woman at the heart of this case, a 25 year old photographer from kaukauna, wisconsin named teresa halbach. >> she just loved being behind the camera. >> kim peterson and teresa became fast friends in college, both were photographers working at the same studio in green bay. kim says teresa had a special way with her subjects. >> she would get the smile. that was one thing, i think, that she really loved to do, was just make other people smile. >> reporter: the two stayed in touch after graduation as they launched their careers. but that would all change suddenly on october 31, 2005. kim caught a story on the local news, teresa was missing. >> investigators say the 25-year-old photographer was on assignment for auto trader magazine when she disappeared. >> and my heart juin someone i knew. >> and what do you do at that moment? >> i felt helpless 'cause you wanna just deny it. you want to try to get in touch with her. >> did you try to call her? >> i did try to text her, but -- >> no response? >> no response. >> reporter: wisconsin police quickly launched a massive search, bolstered by a team of volunteers. after two days, a big break. >> they had found teresa's vehicle on the avery salvage yard. >> reporter: tom fassbender, then a special agent with the wisconsin department of criminal investigation, hustled over to this 40 acre stretch of land in manitowoc county, home to the salvage yard and auto mechanic steven avery. >> had you heard his name before? >> only through the media. >> reporter: steven avery was a big story. he'd been convicted of rape in 1985, but eighteen years later dna evidence exonerated him, and he was freed. a wrongfully convicted man we open arms. and looking for justice of his own. >> were you aware that he had filed a lawsuit against -- >> yes. >> the local sheriff's department? >> yes, i'd heard that. >> reporter: avery hoped winning the $36 million lawsuit could help him get back on his feet. >> he had an opportunity to make something of his life. and it appeared that he was -- he was headed toward -- in that direction. >> reporter: now, two years after his release from prison, this poster boy for wrongful convictions was back in the news and not in a good way. >> i hope she comes back so she can go back to her family. >> reporter: when fassbender arrived on site, he learned teresa halbach had an appointment at the salvage yard on october 31 to take photos of this van avery's sister was selling. teresa had left a message that morning. >> hello this is teresa with auto trader magazine. i'm the photographer and just giving you a call to let you know that i could come out there today. umm in the afternoon, it would probably be around 2 o'clock . >> reporter: steven avery teresa had been on the property that day and left around 2:30 pm. avery didn't tell them much more. but for investigators, a dark tale started emerging from the physical evidence, especially when they made a gruesome discovery in the back of teresa's suv. >> we find teresa's blood in the vehicle, primarily in the cargo area of the rav-4. >> reporter: and in the front, more blood. >> there was blood on some of the upholstery. and then a very telling swipe of blood, near the ignition switch of the vehicle. >> reporter: tests showed that blood was steven avery's, taking him from person of interest to prime suspect. >> you believe you can explain the blood from steven avery? >> well yes absolutely. >> steven avery had a cut on his right hand, middle finger that was freshly scabbed over. and if you took that key and you put it in that ignition switch, it just lined up pct a contact pattern swipe. >> how did he explain that cut? >> i'm not sure if i remember that. i think he had claimed that he had cut it in the junkyard doing work on vehicles. >> reporter: fassbender feared the worst. and after four days of searching, his team found something disturbing in a fire pit near avery's trailer. >> what appeared to be bone fragments. >> reporter: human bones. most interesting because family members told investigators that steven avery had built a bonfire hours after teresa had been at the yard that day. >> it was a huge bonfire. flames going as high as, you know, the edge of the roof on the garage. >> was it all making sense to you? the -- >> looking at -- >> bone fragments. >> the whole picture? absolutely. >> reporter: and that picture came into sharper focus when fassbender's team found another clue, teresa's key, inside avery's bedroom. >> the toyota key with a little fob connector to it. >> yes, it's huge. >> reporter: especially when the crime lab later found avery's dna on it. it would become a highly controversial clue in this case. the evidence was stacking up against steven avery. and fassbender says that rav 4 would later tell investigators one last thing. >> we had tested the -- the hood latch and found dna matching steven on the hood latch. >> reporter: fassbender believed avery had some explaining to do. so nine days after teresa's disappearance, he and his partner mark wiegert brought avery in for an interview. dateline filed a freedom of information request to obtain the video. >> the key is in your bedroom. you know the key is there because you put the key there. that's the only way the key gets there. >> no. >> yes steve. yes. >> reporter: avery was defiant, and even claimed cops were framing him, planting evidence. >> that's the way it is. >>the evidence. cops got the evidence. >> reporter: fassbender and wiegert weren't buying it and placed steven avery under arrest. >> i didn't do it. >> we're not mad at you okay. >> somebody's doing -- somebody's doing a good job on me! >> reporter: investigators were convinced they had their man. still, they didn't know how or why teresa had been killed. >> reporter: in january, 2006, steven avery pleaded not guilty if you've never tried a juicy, cheesy, iconic big mac... it's just right if you want to start smaller. the delicious mac jr, the big mac with a single patty and no middle bun. now available for a limited time only. you can use whipped topping made ...but real joyful moments.. are shared over the real cream in reddi-wip. ♪ reddi-wip. share the joy. i can't work out without n! my music! you need to switch to sprint. i got unlimited data, talk and text for 50 bucks a month! (vo) get unlimited data, talk and text. first line is $50/mo, add a second line for $40, and the 3rd, 4th, and 5th lines are free. that's five lines for $90. for people with hearing loss, switch to sprint. visit sprintrelay.com >> reporter: in january, 2006, steven avery pleaded not guilty to the murder of teresa halbach, began building his case. he chronicles it all in his new book, "avery." >> what do you feel people know the least about in this case? >> the book is about the case against steven avery that is setting forth, a better representation of what the real evidence was. >> reporter: better, he says, than the way the evidence was presented in "making a murderer" for the first time kratz lays out his complete theory of the case with new details he's never shared before. for one thing, kratz tells "dateline" he believes steven avery had set his sights on teresa halbach in the weeks leading up to her murder. >> as we move closer towards october 31st, we see steven's behavior changing. >> reporter: as kratz got auto trader's records he learned teresa had actually made five earlier visits to the avery salvage yard to take photos, some at steven avery's request. >> he starts making calls dily rather than going thh >> reporter: and kratz determined that on the day before one of those visits avery purchased these shackles and handcuffs. and when teresa arrived -- >> he answers the door that day, only wearing a small white towel. and teresa, we know, is -- is creeped out by that behavior. she tells friends and -- and co-workers about that. >> reporter: kratz believes avery's behavior shows signs of a sexual obsession with teresa that led to murder. >> why would steven avery do this when he was on the verge of getting this big windfall, potentially millions of dollars? >> that's a great question. i don't know. we know that he's a psychopath. we know that he has -- >> do we know that? >> well, i -- i -- i -- let's say i allege that. okay? i -- i believe that deep down. >> reporter: kratz discovered more in avery's past. 18 years before teresa's murder, avery wrote this letter to his estranged wife from prison something even more disturbing. this 2006 police report shows a teenage girl accused avery of raping her a year after his release from prison. it all came together for kratz. he believes avery had developed a deep resentment of women which had started with his wrongful conviction, and had only grown over the years. >> he has no remorse for his behavior, feels incredibly entitled. >> reporter: but as he continued to investigate the case, kratz had a problem. >> you still didn't know how she was killed, exactly where she was killed. was that bothering you? >> yes, but sometimes you -- you know, you have what you have. it was all coming together in -- in, bits and pieces. >> reporter: he and his team kept digging until they got a big lead. >> why don't you just have a seat, brendan? >> reporter: in march, 2006, four months after te murder, tom fassbender and his brendan dassey, in a series of now highly scrutinized interviews. >> what was your first impression of brendan dassey? >> a shy kid, somewhat introverted. >> reporter: but once he opened up, the details he revealed would stun investigators. >> what else did he do to her? >> raped her. >> did he tell you that? >> reporter: fassbender says dassey described a brutal scene. on that halloween afternoon, his uncle asked him to come over to his trailer. dassey said they each sexually assaulted teresa in avery's bedroom, and avery later shot her in his garage, burning her body in the bonfire. >> it's a game-changer. he told us stuff that -- that we weren't really aware of like teresa was shot in -- in the garage and had died there. >> reporter: and after speaking with dassey, fassbender had his team return to the avery property once more. and they found this in his garage, a bullet fragment. >> and that was missed the first time around? >> well i gui but you're talking about bullet fragment, .22 bullet fragment. looks like a piece of dirt possibly. >> it was tested? >> it was tested. >> yes. teresa's dna was on that bullet, and the bullet from shot from steven's rifle or the one above his bed. >> do you now believe that teresa was shot in that garage? >> yes. >> reporter: one strange thing, though, when they searched the garage for blood, they never found a drop. >> how could you clean up all that blood? >> oh, he did it to the best of his ability, i guess. bleach, paint thinner, that cleans up blood. >> reporter: teresa's friend kim says when she heard the details about teresa's final moments, she was heartbroken. >> i remember crying and just hoping she was who she was and fought because she was a very strong person. >> reporter: ken kratz charged brendan dassey as a these defendants accountable for the rape, the torture, and the murder of teresa halbach. >> reporter: but, not so fast. dassey recanted his statements just before avery's trial, the judge dismissed the rape charge against him and didn't allow any of those allegations about avery's treatment of women, saying they didn't prove anything about teresa's murder. and avery was never charged with assaulting his ex-fiance or with raping the teen. to this day, he denies all the allegations. and those handcuffs and shackles? no evidence ever linked them to teresa. still, in the spring of 2007, juries in separate trials convicted both dassey and avery of murdering teresa. they were each sentenced to life in prison. >> you are probably the most dangerous man ever to enter my courtroom. >> reporter: it seemed like the avery saga had ended. but eight years later, "making a murderer" would put fassbender, kratz, and their entire team in the hot seat. sangre?. >> was steven avery framed. >> is it possible the blood could have been planted. >> a lead investigator answers allegations for the first time. >> did you have any vendetta against steven avery. >> absolutely not. >> when the dateline continues. together, we are perfectly balanced, our senses awake, our hearts racing as one. i know this is sudden, if you love something... set it free. see you around, giulia ♪ choose your favorite pasta,or piadina or sandwich. it all comes with our never-ending soup or salad. and all the breadsticks you want. starting at just $6.99 get never-ending value for lunch, today at olive garden. my hygi...a mouthwash.o try... so i tried crest. it does so much more than give me fresh breath. crest pro-health mouthwash provides all... ...of these benefits to help you get better dental check-ups. go pro with crest mouthwash. checkup? nailed it c'mohappy birthday! i survived a heart attack. i'm doing all i can to keep from having another one. milligramspeople who've been as it affects how well it works. brilinta helps keep my platelets from sticking together and forming a clot. brilinta reduced the chance of another heart attack. or dying from one. it worked better than plavix. don't stop taking brilinta without talking to your doctor since stopping it too soon increases your risk of clots in your stent, heart attack, stroke, and even death. brilinta may cause bruising or bleeding more easily, or serious, sometimes fatal bleeding. don't take brilinta if you have bleeding, like stomach ulcers, a history of bleeding in the brain, or severe liver problems. tell your doctor about bleeding, new or unexpected shortness of breath, any planned surgery, and all medicines you take. talk to your doctor about brilinta. i'm doing all i can. that includes brilinta. if you can't afford your medication, astra zeneca may be able to help. >> reporter: in december 2015, netflix released "making a enforcement. >> who would wanna set you up in >> the only thing i can think of is manitowoc county with the money. so, they didn't have to pa nothing out. >> did they plant evidence? sure they did. >> reporter: kim ducat is avery's cousin. she says she had predicted something bad might happen to him after he was exonerated in that earlier rape case. remember he had recently filed a lawsuit against his local sheriff's department for his wrongful conviction. >> i did tell him manitowoc wasn't done with him. >> why did you think they weren't done with him? >> just something just told me they weren't gonna hand that steve avery $36 million or any kinda money, that they were just going to be watching him. // and look what happened. >> reporter: avery ended up settling that lawsuit for 400 thousand dollars before his trial. the county did not acknowledge any wrongdoing. he used the money to hire his defense attorneys dean strang and jerry buting. >> we knew going in it was going to be a difficult defense. >> reporter: we spoke to buting early last year. >> we had a very tough defense in this case because nobody wants to try and use as a defense that the police deliberately tried to plant that's not -- >> it go -- it goes against society. >> it's very difficult. >> those -- those are -- those people are there to help us. they're the police. >> right. but it's where we thought the evidence pointed. >> reporter: avery's attorneys believed the fact that officers from the county he was suing were part of the search made for a huge conflict of interest. and for possible mischief at the crime scene. >> what i can say is from the evidence i've looked at, i -- i think he was innocent, is innocent. >> reporter: preparing for trial, buting learned about a vial of avery's blood left over from his overturned rape conviction, which had been sitting in the manitowoc county clerk's office. >> we saw that there was still a styrofoam box that had been slit open with evidence tape. >> that's really the big "aha" moment. >> yeah, it was. >> reporter: and for many viewers it was the "aha moment" in "making a murderer." >> a little tiny hole. >> reporter: the attorneys theorized that someone could have poked and spread avery's blood inside teresa halbach's suv. as for teresa's car key -- >> your theory is that the key was planted in the residence? >> that is where we thought the evidence pointed, yes. >> by the police? >> by someone. you know, it was not found in, you know, six or seven earlier entries to the trailer. and we're talkin' about a trailer, it didn't add up. >> reporter: co-lead investigator tom fassbender worked alongside the local county sheriff's deputies but was employed by a different agency, the wisconsin department of justice. this is the first time he's responded publicly to the accusations against him and his law enforcement colleagues. >> did you have any kind of vendetta against steven avery? >> abso -- >> or his family? >> absolutely not. i -- i didn't know steven avery. i didn't know his family. never been there. >> reporter: fassbender bristles at the idea the local investigators could have done anything unethical. >> the people that were there that i worked with from manitowoc county were hard working. they only wanted to do the right investigation the right way. be? >> no. everything -- all the evidence says no. >> reporter: fassbender notes that a chemical called edta had been used to preserve avery's blood in the vial, and that at trial tests showed no presence of edta in avery's blood found in the suv. >> didn't match. no edta in the blood in the vehicle. >> reporter: fassbender's argument? since that blood found in the vehicle didn't contain the chemical, it couldn't have come from the vial. and he notes that a nurse was prepared to testify she had made that hole in the vial as part of her usual routine when she drew the blood from avery. >> so the fact that there is a little hole in the top of the -- the vial is normal. >> reporter: and regarding teresa's car key, not found until the seventh search of avery's trailer -- >> why was the key missed during those other searches? the key was located in -- in small bookcase -- that wasn't searched yet. and if it was, it was just kinda looked at. >> why not do the thorough search earlier? >> oh, i would guess part of it is because we didn't lock and load on steven avery. you know, we went in there, did that -- that first search. but we had 12 more buildings and four more residences to search. so we had a lot to do. >> reporter: still, it wasn't just when the key was found that has avery's supporters skeptical. it's who found it, these two men, lt. james lenk and sgt. andrew colborn, of the manitowoc county sheriff's department. it turned out they had just been deposed in avery's lawsuit. >> well, they were deposed -- that we later found out -- >> so do you think though -- >> they were deposed. >> that maybe just them, by nature, being with manitowoc that maybe they shouldn't have been in there at all just to avoid all of this speculation. >> it's easy to armchair quarterback and -- second guess. i think we would've done that maybe if we had the resources. but you're talking about a small rural county being assisted by another smaller rural county. you need resources. >> steven avery said -- says, "these guys had it out for me. the whole department was angry at me. this was the perfect opportunity for them to have access to my trailer, plant the key." >> i never absolutely saw that. never -- never saw that from anyone in manitowoc county. >> reporter: fassbender says he believes a conspiracy to frame avery would have been virtually impossible to carry out. >> i could go on and on about -- the -- the planting defense and how absurd it is, with the multiple agencies that we had in there. >> i'm your friend right now. >> reporter: but it was that video of brendan dassey which would really put fassbender at the center of the storm. an interrogation so controversial it might get avery's nephew out of prison. coming up. how much of brendan daisy east >> those officers wanted that information in the worst way and they got it in the worst way. oh yai yai yai yai yai yai. look at the moon. whoot. what bad back?gels work so fast you'll ask what pulled hammy? 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>> no, no. i don't even think he knew what that was at the time. >> reporter: in 2008, attorneys steven drizin and laura nirider took up dassey's case for his appeal. they saw a mentally challenged teen with a low iq. >> how do you spell garage? >> g-a-r. >> yeah. >> a-g-e. >> what did you think of brendan dassey when you were finally able to meet him in person? >> brendan is a simple soul. i was struck by his humanity. th committing a crime like this. >> that's the psychological power of interrogation. >> reporter: the two attorneys are based at the northwestern university school of law outside chicago. they've worked to free a number of wrongfully convicted defendants, and say what they learned about dassey's case astounded them. >> nobody was in brendan dassey's corner at the moment he needed help the most. >> reporter: beginning, they say, with this man. >> give me one word to describe len kachinsky. >> unbelievable. >> unconscionable. >> reporter: len kachinsky came on board to defend dassey just after that interrogation got avery's nephew arrested. drizin and nirider discovered that the attorney had made legal mistakes that caused him to be removed from the case. he has faced online vitriol from dassey supporters. >> is it okay if i read you some of the comments? >> sure, sure, go ahead. >> "disgusting human being, a pure disgrace to the wisconsin judicial system, a man with a sickened soul." >> i've se i [ laugh ] >> reporter: in one instance, kachinsky, working to cut a plea deal while dassey was in jail, had arranged for his client to speak with investigators, but kachinsky, himself, didn't show up. >> tell me what the truth is. >> that i stabbed her in the stomach. >> that was clearly a mistake. >> this is huge, though. i mean, you've got -- >> i agree. >> a 16-year-old kid with a low iq with no attorney present, no parent. >> i'll say. >> it's kind of like feeding someone to the wolves in a way. >> would you apologize to brendan dassey. >> well, i'd apologize -- apologize to him for not being at that interview. >> so there were mistakes made? >> oh sure, there were mistakes, but none of them contributed to the verdict in dassey's case. >> there are people who disagree with that. >> oh sure. >> reporter: but as dassey's attorneys delved further into those stunning statements the teen made, they came to believe something more disturbing, that investigators tom fassbender and mark wiegert had coerced the teen into making a false confession. say. >> don't lie to us now okay. come on. what happened? >> you're just hurting yourself if you lie now. >> he's got severe learning disabilities, inability to respond in a narrative type answers. and they're in precisely the areas that make him vulnerable to the kind of tactics that the police officers used in this case. >> reporter: the attorneys say that the investigators manipulated dassey with coaxing statements like these from fassbender, who was seated just off camera. >> i'm your friend right now. it's all right. you are doing the right thing. >> they should never have made those kinds of suggestions that they wanted to comfort him, that all would be well. those kinds of tactics when used on a kid like brendan are a recipe for false confessions. >> reporter: and they say the investigators' manipulation of the teen escalated far beyond simple coaxing. >> the officers needed brendan to provide information that only the real killer would know, and they knew what they wanted him to say. >> reporter: they accuse the investigators of planting details about the crime in dassey's mind to get the answers they wanted. for example, remember steven avery's dna found on the car hoodlatch? the attorneys say investigators asked dassey leading questions to confirm that his uncle had looked under the hood of the car. >> did he raise the hood at all or anything like that, to do something to that car? >> yeah. >> what did he do under the hood, if that's what he did? >> i don't know what he did, but i know he went under. >> reporter: and dassey's attorneys say in that same interview the investigators used another crucial detail they'd learned about the case from the >> tell us what else did you? something with the head. >> they had received a report from the wisconsin crime lab indicating for the first time, how teresa halbach had died. she had been shot in the head. they worked extremely hard to get brendan to say that. >> we have the evidence brendan. we just need you to, to be honest with us. >> that he cut off her hair. >> what else was done to her head? >> that he punched her. >> what else? it's okay. what did he make you do? >> cut her. >> what else happens to her in her head? >> it's extremely, extremely important you tell us this, for us to believe you. >> come on, brendan. what else? >> that's all i can remember. >> all right, i'm just gonna come out and ask you. who shot her in the head? >> he did. >> why didn't you tell us that? it. >> those officers wanted that information in the worst way, and they got it in the worst way by feeding it straight to brendan dassey. >> even they know that that's bad police practice. >> reporter: then drizin and nirider discovered something at the end of that interview which was a revelation to them, something jurors in his trial never heard, dassey speaking to his mother. >> i never did nothing or something. >> did you? huh? >> not really. >> what do you mean not really? >> they got to my head. >> huh? >> at the first moment that brendan gets outside the influence of those interrogators, he says, "no, this is not true. they got to my head." >> reporter: but tom fassbender, the interrogator himself, sees it all very differently. he's defending his tactics publicly for the first time. coming up, fassbender responds. this was seen by many as a host confession. >> he knew right from wrong. brendan was involved in this. a better moment of proof. victoza lowers my a1c and blood sugar better than the leading branded pill, which didn't get me to my goal. victoza® works with your body to lower blood sugar in three ways: in the stomach, the liver, and the pancreas. and while it isn't for weight loss, victoza® may help you lose some weight. non-insulin victoza® comes in a pen and is taken once a day. 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er than she should. new olay regenerist helps take years off your skin age so you can look younger. who needs dna when you have olay? new regenerist. >> reporter: for his interrogation of brendan dassey, now seen by millions, tom fassbender has come under fire in court and online. >> this was seen by many as a false confession. do you see it as a false confession or a real confession? >> i feel it was a real confession. >> were you ever trying to extract a false confession from him? >> absolutely not. >> reporter: fassbender denies that his expressions of sympathy for dassey were manipulative. >> i legitimately was concerned for him. that wasn't staged. that wasn't strategy. >> why do you think people took it the other way, the -- the more sinister way, that you were taking advantage of him? >> i think that's easy to do. the -- the -- from -- it's a cynical approach, so to speak, watching tv, watching movies, how cops are depicted on those movies, trying to trick people into saying stuff. everything about the interview with brendan was soft, was comfortable. >> reporter: but comfortable might not be a word dassey's supporters would use, especially level. >> what about his iq? because when you watch him, you can tell that he has a lower iq. >> i don't -- [ chuckle ] i -- i don't assess iqs. i mean, i'm not, you know -- >> but could you tell that he maybe wasn't like other boys his age? >> more socially, probably. you know, i -- i -- i don't want to cross the iq social line. but he could think, and he knew right from wrong. >> is it possible that he's easily manipulated? >> it's possible. >> he sounded confused at times? >> quite possibly. >> he didn't know what was up and down. i don't know, just watching it. >> i don't know about that. my thought is he had a million things going on in his -- his head at that time. >> reporter: fassbender resists charges that he and his partner inappropriately planted ideas in dassey's head, like in that exchange about the hoodlatch. >> what did he do under the >> what did brendan say? >> you used the word, "agreed"? >> yes. >> so you brought it up first? >> yeah, i -- i believe so. >> and that's -- that's one of the areas that you came under fire for? >> yes. >> is that you were planting things in this mind? >> yes, that's -- >> what they said. and there were instances that we did ask him specifically about things, yes. and that can happen in an interview. >> can we take that as a reliable answer, given how it was spoon-fed to him? >> no. their side would argue no. and i would say based on the -- the entirety of the interview, i would say yes. >> reporter: and as for that other moment that has angered so many followers of the case. >> all right, i'm just going to come out and ask you. who shot her in the head? >> he did. >> any regrets about that, bringing it up yourselves, about putting that in his head? brendan's personality that, yeah, we -- we had to talk to him about and -- and ask more specifically certain questions. and -- and that happens. >> what do you say to those people who've made you part of this big discussion about false confessions and who were yelling at their tvs because they didn't like the job that you did? >> just that it's easy to armchair quarterback. it's easy to second guess. that i -- you know, i -- that -- that's partly why i'm here, is explain that there was nothing nefarious done. >> reporter: but even fassbender wonders if everything dassey said in the confession was true. >> we didn't try to manipulate brendan. we tried to get at the truth, and i don't believe that it was a false confession. are there parts of it that he may have not done? i -- i don't know. you know, i just don't know. >> reporter: last august, a federal judge weighed in with a bombshell. in response to a brief filed by dassey's attorneys, judge william duffin ruled that brendan dassey's confession was "involuntary." with that, the judge overturned his conviction and ordered dassey to be released from prison. >> what was that like for you, hearing that news? >> mixed emotions. i know we did everything above board. one magistrate rules that it isn't fine, in his opinion, which is all right because that's the system. >> are you okay if he walks free? >> i'm not okay if the family's not okay. i believe brendan was involved in this, that he was there and he was involved in it. >> reporter: brendan dassey is now 27. his release is pending an appeal from the wisconsin attorney general, which was jusar meanwhile, the other half of this saga is playing out in state court, and steven avery's attorney is leaving no stone unturned. coming up, the latest. i'm out of data again! i can't work out without my music! you need to switch to sprint. i got unlimited data, talk and text for 50 bucks a month! and text. first line is $50/mo, add a second line for $40, and the 3rd, 4th, and 5th lines are free. that's five lines for $90. for people with hearing loss, switch to sprint. visit sprintrelay.com ♪ share the joy of real cream... ...with reddi-wip. so we know how to cover almost alanything.ything, even a "truck-cicle." 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[burke] and we covered it, february fourteenth, twenty-fifteen. talk to farmers. we know a thing or two because we've seen a thing or two. ♪ we are farmers. bum-pa-dum, bum-bum-bum-bum ♪ but with this usp seal i know seaexactlyap. t gummy certified by usp. a non profit organizat that sets purity and potency standards. something bigger.here. and something... smaller. juicy. lettuce-y. onion-y. cheesy. iconic big mac®. now in three sizes, for a limited time only. ♪ ba da ba ba ba more "doing chores for dad" per roll more "earning something you love" per roll bounty is more absorbent, so the roll can last 50% longer than the leading ordinary brand. so you get more "life" per roll. bounty, the quicker picker upper >> reporter: as brendan dassey awaits his fate, steven avery and his supporters hope for good news in his case. >> he's very gentle and very loving. >> reporter: sandy greenman is avery's longtime friend -- and onetime fiance. convinced of his innocence, she says she searched for years to find the right attorney to take on his complicated case. during a call from prison, avery told her to watch dateline. >> he had heard that there was going to be this ryan ferguson case on dateline. and so he told me to watch it just to see the lawyer. >> reporter: that dateline program, from august 2011, told the story of ryan ferguson, a young man sitting in prison for a murder he said he didn't commit. attorney kathleen zellner was determined to get him out. >> nothing's as riveting as this. when the trial's been lost, everything's been lost, and who's innocent, it's like the ultimate challenge, i think. >> i said "that's the woman that's going to get steven out of prison." >> reporter: zellner specializes in wrongful conviction cases, and says she has freed eighteen defendants, including ryan ferguson. sandy contacted her, and she joined the case not long after making a murderer came out. >> reporter: we caught up with zellner at the waupun correctional institution when she paid a visit to avery early last year. >> million dollar question. do you think you have new evidence that could free steven avery? >> we do. yeah. >> reporter: zellner invited dateline into this 'war room' she created in her office outside of chicago -- all dedicated to the avery case. >> do we know if that was tested? >> reporter: and she even showed us this rav4 she bought, to get a better understanding of teresa's vehicle. then in august, to much media fanfare she filed a motion in manitowoc county court seeking new testing of the evidence. >> we're going to find out one way or the other, was the evidence planted. >> kathleen zellner is known as an aggressive defense attorney. >> reporter: ari melber is chief legal correspondent for msnbc. >> she's looking for new evidence to argue the entire case was done the wrong way. she's basically trying to put the state on trial. >> reporter: in her 45 page legal motion, zellner attacks law enforcement, tries to poke holes in the prosecution's case, and raises new questions. >> she notes that teresa's cell phone pinged off a cell phone tower 13 miles away later that day, suggesting maybe she left there alive. there's also indications that other people not from law enforcement entered the property during the investigation, raising the prospect of other potential suspects. >> reporter: and she's won an early round. in november a judge granted her access to some of the evidence so her experts could perform new forensic tests, including more advanced testing on avery's blood from the rav4.ellner woul be evidence to show that the blood from the car wasn't from a fr avery but rather from that older blood sample. >> reporter: in a statement zellner recently told dateline: "we will be able to demonstrate exactly how the evidence was planted in the early part of the investigation." avery, she insists, was "framed for a crime he did not commit." as for former prosecutor ken kratz and his new book, zellner dismisses kratz's claims about avery's treatment of women and interactions with teresa, saying "there was no proof that mr. avery was becoming obsessed with ms. halbach." and that "rehashing a story about inadmissible evidence seems pointless." ' zellner also notes: "mr. kratz has no qualifications which would allow him to diagnose mr. avery as a psychopath. mr. avery has never been diagnosed as a psychopath." >> reporter: kratz, who prosecuted both steven avery and brendan dassey, says he's undaunted. >> are you afraid of kathleen zellner? >> no. i'm not involved in the case anymore. i shouldn't be afraid of -- of anything. my involvement -- >> she could -- >> concluded -- go ahead. >> she could unravel your work if what she's saying has some weight to it. >> you don't think she has a chance? >> i don't. >> she's so confident; why are you so confident? >> because we spent 18 months putting this case together. this wasn't just thrown together. it wasn't a bunch of keystone cops. it was done very professionally, very well. >> reporter: kratz does have personal regrets. in his book he admits to past prescription drug abuse, and says he's ashamed that he sent sexually suggestive texts to a domestic violence victim -- two years after avery's trial. a scandal which led to his resignation. while he still takes issue with "making a murderer," he says he's moving on with his life. >> i'm hoping -- this book will change the narrative. >> reporter: meanwhile, avery continues to fight. and brendan dassey could be released soon, after more than a decade behind bars, perhaps for a new trial. but with all the talk of guilt or innocence, trials or retrials, kim peterson says that the person being forgotten is her friend, teresa. >> she is the reason why we're even talking about this. and she just deserves to be remembered. >> reporter: for her memories kim says she goes back to this grainy video diary teresa made three years before she died. it was played at avery's sentencing. >> i love taking pictures. i love holding a camera in my hand. >> it gives me the chills every time i hear it. because she talked about everything she loved. >> is there an say to teresa right now if she could hear you? >> just that, you're still in my heart. and i'll never forget you. >> i just want to know that whenever i do die, i just want people i love to know that whenever i die, that i was happy. that's all for this edition of dateline. see you norm 8, 7 central. and, again, sunday. i'm lester holt. from all of us at nbc news, good night. now at 11:00, it's happening again. big scores at some of our area's priciest retailers. thieves armed with pepper spray. tonight, one woman shares her frightening encounter. >> searching for the person who killed a man on