"We believe the magistrate judge's decision that Brendan Dassey's confession was coerced by investigators, and that no reasonable court could have concluded otherwise, is wrong on the facts and wrong on the law", Schimel said in a statement. In November of past year, a Milwaukee judge finally recognized that and made a decision to overturn Dassey's conviction, granting him supervised release from prison while the state decided it it wanted to pursue a retrial.
The state of Wisconsin has 90 days to retry Dassey or the decision becomes final.
"[We] hope that today's erroneous decision will be reversed", a spokesman for the state's department of justice told the Milwaukee Journal Sentinel.
The state Justice Department appealed the ruling to the 7th US Circuit Court of Appeals.
During two separate police interrogations, he confessed to helping Avery, his uncle, rape and kill Halbach, 25, who went missing on October 31, 2005.
But the 27-year-old, one of two men serving life sentences featured in the Netflix series, could face a re-trial after a panel of three judges on Thursday ruled against the U.S. prosecutors' appeal. A three-judge panel from the 7th Circuit on Thursday affirmed the lower court and said Dassey should be freed unless the state chooses to retry him.More news: Yukon bar gets its notorious human toe back
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Duffin ordered Dassey freed in November, but his release was halted while Wisconsin authorities appealed the decision.
The case was the subject of the hit docu-series "Making a Murderer", a Netflix production that was released in December 2015.
Brendan Dassey is pictured in this undated booking photo obtained by Reuters January 29, 2016. Avery spent 18 years in prison in that case before DNA tests showed that he didn't commit the crime.
He concluded that, "when considered in conjunction with all relevant factors, most especially Dassey's age, intellectual deficits and the absence of a supportive adult, rendered Dassey's confession involuntary".
April 25, 2007: After 4½ hours of deliberation, the jury convicts Dassey of being party to first-degree intentional homicide, mutilation of a corpse and second-degree sexual assault. Dassey had stated, very unconvincingly, that he had aided his aforementioned uncle (who also received a life sentence) in the rape and murder of Halbech in their family auto salvage yard.
Dassey offered conflicting versions of his story, according to the appeals court opinion.
Attorney Laura Nirider said they want to send Dassey home to his mother as soon as possible. However, the legal system is not kind to convicts, even with the benefit of hindsight, and Dassey will still need more than a little help if the state decides to put his case back in the courtroom.