FILE - In this Friday, March 3, 2006 photo, Brendan Dassey, 16, is escorted out of a Manitowoc County Circuit courtroom in Manitowoc, Wis. A federal court in Wisconsin on Friday overturned the conviction of Dassey, a man found guilty of helping his uncle kill Teresa Halbach in a case profiled in the Netflix documentary "Making a Murderer." (AP Photo/Morry Gash, File)
FILE - In this Friday, March 3, 2006 photo, Brendan Dassey, 16, is escorted out of a Manitowoc County Circuit courtroom in Manitowoc, Wis. A federal court in Wisconsin on Friday overturned the conviction of Dassey, a man found guilty of helping his uncle kill Teresa Halbach in a case profiled in the Netflix documentary "Making a Murderer." (AP Photo/Morry Gash, File)

A federal judge in Wisconsin on Friday overturned the conviction of Brendan Dassey, a figure in the Steven Avery case, which was featured in the Netflix documentary series Making a Murderer.

In his 91-page filing, U.S. Magistrate Judge William Duffin wrote that the 26-year-old Dassey, who is Averyโ€™s nephew, should be released from custody unless the state decides to retry him within 90 days. The state could also appeal Fridayโ€™s ruling, said Laura Nirider, Dasseyโ€™s attorney.

โ€œHeโ€™s in shock,โ€ Nirider told The Washington Post in a phone interview Friday night, when asked about her clientโ€™s reaction. โ€œHeโ€™s grateful and I think just trying to process and understand whatโ€™s happening, as I think we all are.โ€

Duffin wrote that state courts had โ€œunreasonably found that the investigators never made Dassey any promisesโ€ during an interrogation in March 2006.

โ€œThe investigators repeatedly claimed to already know what happened on October 31 and assured Dassey that he had nothing to worry about,โ€ the order states. โ€œThese repeated false promises, when considered in conjunction with all relevant factors, most especially Dasseyโ€™s age, intellectual deficits, and the absence of a supportive adult, rendered Dasseyโ€™s confession involuntary under the Fifth and Fourteenth Amendments.โ€

A spokesman for the Wisconsin Department of Justice declined to comment, saying in an email that the agency was reviewing the order.

โ€œIโ€™m thrilled. Brendanโ€™s entire team is over the moon,โ€ Nirider said. โ€œThis is the right result. Itโ€™s justice. Itโ€™s justice for Brendan. Itโ€™s justice for his mother. And itโ€™s justice for anyone who cares about the truth in this case.โ€

In its report on the ruling, the Milwaukee Journal Sentinel noted that Duffin โ€œwas highly critical of investigators, Dasseyโ€™s pretrial attorney and the state courts on how they handled the case, concluding that Dasseyโ€™s constitutional rights were violated.โ€

โ€œThis is a 91-page opinion,โ€ Nirider said. โ€œAnd the court got it exactly right.โ€

Steven Avery and Dassey were convicted in the 2005 murder of Teresa Halbach, a 25-year-old photographer. Averyโ€™s story was the focus of Making a Murderer, a 10-episode documentary series from Netflix that was released in December. Hereโ€™s The Postโ€™s Bethonie Butler, breaking down Dasseyโ€™s role in the Avery case:

The case against Avery took a shocking turn when his 16-year-old nephew implicated himself in the murder and told police that Avery had instructed him to rape Halbach and to help him dispose of her body.

The documentary describes Dassey as learning disabled โ€” during his trial, one of his attorneys reported that he reads at a fourth-grade level. Throughout the series, Dasseyโ€™s story changes dramatically as he undergoes a series of questionable interrogations, some of which were encouraged by his court-appointed pretrial attorney, Len Kachinsky. Kachinsky was eventually removed from Dasseyโ€™s case after allowing his client to be interrogated by police without a lawyer present.

At his trial, Dasseyโ€™s attorneys argued that their clientโ€™s confession was false, and the teen repeatedly said he fabricated his statements under pressure from law enforcement. In April 2007, Dassey was convicted of homicide, sexual assault and mutilation of a corpse.

Avery was convicted of first-degree intentional homicide and being a felon in possession of a firearm in 2007. Later that year, he was sentenced to life in prison. Dassey had also been sentenced to a life term.