letter he read as part of the netflix documentary. >> i am innocent of the rape and murder of teresa holback. please help me if you can. >> reporter: i set out to explore the question, if brendan dassey did not commit the crime, why would he confess? if this videotape really shows dassey falsely confessing what made the jury convict? >> we're going to laura's office. >> reporter: laura nye ryder. >> they're not banging the table, they're not threat ning him. does it fit into the classic model of coercive interrogations? >> absolutely, it does. >> reporter: at the time of his arrest branagan was a high school he had a low iq and was enrolled in special ed classes. he lived on the family salvage yard next to his uncle steven. who had been released from prison after serving 18 years for a rape he didn't commit. >> we're glad you're home, honey. >> reporter: then avery was arrested and charged with the murder of teresa holback. >> just have a seat. >> reporter: several months >> cut her where? >> on her throat. >> it appeared hard to be able to argue it was coerced. >> reporter: len kachinsky wa

the teenager from wisconsin describing how he and his uncle murdered 25-year-old photographer teresa holback. today a stunning reversal. after nearly a decade behind bars a federal judge overturned his conviction, ruling the teen's confession was involuntary because investigators pushed him into it. dassey's trial was featured in netflix's true crime documentary sensation "making a murderer." the case sparked outrage among many viewers and dassey's defense team, who said that the crime he did not commit. a lawyer who starred in "making a murderer" tweeting today, justice finally strikes. >> we're over the moon. >> reporter: laura nye ryder, one of dassey's lead attorneys and fiercest defenders. >> he's in shock. he's grateful. he's trying to process and understand what's happening. >> come on branagan, be honest. you can do it. tell us the truth. >> reporter: the judge today acknowdg reliability of dassey's confession but said the ruling hinged on whether the confession was given voluntarily, and based on dassey's age, intellectual deficits, and the absence of supportive adults, he determine

rape he didn't commit. >> we're glad you're home, honey. >> reporter: then avery was murder of teresa holback. >> just have a seat. >> reporter: several months later brendan was brought in for questioning. >> cut her. >> cut her where? >> on her throat. >> it appeared hard to be able to argue it was coerced. >> reporter: len kachinsky was one of dassey's original court-appointed attorneys. he says when he watched the confession tape he became convinced there was no way a jury would believe dassey was innocent. kachinsky did try to get >> the defendant's motion to suppress these statements is denied. >> what are your thoughts? >> we're disappointed. we're going to start over. >> reporter: kachinsky cut a plea deal, set up another interview with his client and the police. >> you and steve had this planned? yeah? yes or no? >> yeah. >> reporter: an interview kachinsky actually skipped because he says he had army >> with 20/20 hindsight, yeah, it was a mistake. >> reporter: for his failure to attend that meeting -- >> okay, why don't you sign that? >> reporter: the judge removed kachinsky from da