The confession of a Wisconsin inmate featured in the Netflix series Making a Murderer was improperly obtained and he should be retried or released from prison, a three-judge U.S. federal appeals panel ruled.

Brendan Dassey was sentenced to life in prison in 2007 in photographer Teresa Halbach's death on Halloween two years earlier. Dassey told detectives he helped his uncle, Steven Avery, rape and kill Halbach in the Avery family's Manitowoc County salvage yard. Avery was sentenced to life in a separate trial.

A federal magistrate judge ruled in August that investigators coerced Dassey, who was 16 years old at the time and suffered from cognitive problems, into confessing and overturned his conviction. The state Justice Department appealed the ruling to the 7th U.S. Circuit Court of Appeals, a move that kept Dassey, now 27, behind bars pending the outcome.

A three-judge panel from the Chicago-based 7th Circuit on Thursday upheld the magistrate's decision to overturn his conviction. Wisconsin can appeal to the U.S. Supreme Court, ask for a review by the full 7th Circuit or retry Dassey within 90 days.

Johnny Koremenos, a spokesman for Wisconsin Attorney General Brad Schimel, said the office expects to seek review by the full 7th Circuit or the U.S. Supreme Court, and hopes "that today's erroneous decision will be reversed."

"We continue to send our condolences to the Halbach family as they have to suffer through another attempt by Mr. Dassey to re-litigate his guilty verdict and sentence," Koremenos said.

Dassey's lawyers from the Center on Wrongful Convictions of Youth at Northwestern University said they're elated and will take immediate steps to secure his release.

Attorney Laura Nirider said they want to send Dassey home to his mother as soon as possible. She said they did the math and determined that he had been in prison for 4,132 days as of Thursday.

Dassey was 'clearly overwhelmed,' says attorney

The center's director, Steven Drizin, said the ruling provides a model for the kind of thorough analysis that courts should always undertake in assessing whether a confession was voluntary, and highlights the importance for teenagers to have parents or trusted adults in the interrogation room.

'While these tactics might not have overwhelmed a seasoned criminal or a 30-year-old with a law degree, they clearly overwhelmed a 16-year-old.' - Steven Drizin

"While these tactics might not have overwhelmed a seasoned criminal or a 30-year-old with a law degree, they clearly overwhelmed a 16-year-old, socially avoidant, intellectually limited [youth] who had never been interrogated by the police before," he said.

The appellate panel split, with Judges Ilana Rovner and Ann Williams affirming and David Hamilton in dissent. The majority opinion by Rovner said "no reasonable court" could have any confidence that Dassey's confession was voluntary. It cited "the leading, the fact-feeding, the false promises, the manipulation of Dassey's desire to please" as among many factors that cast it in doubt.

Hamilton, in dissent, wrote: "The majority's decision breaks new ground and poses troubling questions for police and prosecutors. It calls into question standard interrogation techniques that courts have routinely found permissible, even in cases involving juveniles."

TV Avery Lawyers Tour 20160229

Steven Avery, seen in 2007, contends he was framed by police angry with his lawsuit for an earlier wrongful conviction for sexual assault. (Morry Gash/Associated Press )

Avery and Dassey contend they were framed by police angry with Avery for suing Manitowoc County over his wrongful conviction for sexual assault. Avery spent 18 years in prison in that case before DNA tests showed he didn't commit the crime. He's pursuing his own appeal in state court.

Their cases gained national attention in 2015 after Netflix aired Making a Murderer, a multi-part documentary looking at Halbach's death, the ensuing investigation and trials. The series sparked widespread conjecture about the pair's innocence and has garnered them a massive following on social media pushing for their release.

Authorities who worked on the cases insisted the documentary is biased. Ken Kratz, the prosecutor, wrote in his book Avery that Dassey was "a shuffling, mumbling young man with bad skin and broken-bowl haircut" who could have saved Halbach's life but instead involved himself in her rape and murder and Avery is "by any measure of the evidence, stone guilty."

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Key events in the case:

Oct. 31, 2005: Teresa Halbach, 25, of St. John in Calumet County, a photographer for Auto Trader Magazine, goes to Avery's Auto Salvage near Mishicot to photograph a minivan for sale by Steven Avery's sister. Evidence later shows Avery called asking for her to come, using his sister's name.

Nov. 3, 2005: Halbach's family reports her missing.

Nov. 5, 2005: Halbach's cousins find her vehicle under brush and auto parts in the Avery salvage yard. Charred bone fragments found in a burn pit later are determined to be her remains.

Nov. 8, 2005: Avery tells reporters he fears authorities are trying to frame him for Halbach's slaying because he sued Manitowoc County officials for $36 million for wrongful conviction. Avery spent 18 years in prison for rape before DNA evidence cleared him of the crime and he was freed in 2003.

Nov. 9, 2005: Avery is arrested and, based on past convictions for burglary and other crimes, charged with possessing firearms as a felon. Authorities say two guns were in his trailer home.

Nov. 15, 2005: Avery is charged with first-degree intentional homicide and mutilating a corpse.

Feb. 14, 2006: Authorities announce Avery has settled his lawsuit against Manitowoc County officials for $400,000.

March 2, 2006: Avery's nephew Brendan Dassey, then 16, is charged in adult court with being a party to first-degree intentional homicide, mutilation of a corpse and first-degree sexual assault. Prosecutors base the charges on a videotaped statement in which Dassey detailed the killing, saying he and Avery raped and killed Halbach and burned her body. He later recants the statement.

Jan. 29, 2007: A judge dismisses sexual assault and kidnapping charges against Avery because Dassey may not testify at his trial.

Jan. 30, 2007: A judge says defence attorneys can tell jurors that Avery was wrongfully convicted of rape and may use as evidence a vial of his blood found unsecured in the Manitowoc County courthouse. Defence attorneys say discovery of the vial supports their claim that blood was planted to frame Avery.

Feb. 12, 2007: Avery's trial begins.

March 12, 2007: After the prosecution and defence rest, the judge dismisses the false-imprisonment charge, saying he doesn't think the jury has enough evidence to find Avery guilty. Avery has not taken the witness stand. Dassey also does not testify in Avery's trial.

March 18, 2007: After deliberating for nearly 22 hours over three days, jurors convict Avery, now 44, of first-degree intentional homicide and being a felon in possession of a firearm. Avery is acquitted of the charge of mutilating a corpse.

April 16, 2007: Dassey, now 17, goes on trial before a jury selected in Dane County.

April 20, 2007: Prosecutors play Dassey's videotaped confession for the jury.

April 23, 2007: Dassey testifies in his own defence, saying he lied when he gave the statement but doesn't know why. Avery does not testify.

April 25, 2007: After 4 1/2 hours of deliberation, the jury convicts Dassey of being party to first-degree intentional homicide, mutilation of a corpse and second-degree sexual assault. Sentencing is scheduled Aug. 2.

June 1, 2007: Avery is sentenced to life in prison with no possible parole.

Aug. 2, 2007: Dassey is sentenced to mandatory life in prison with a possibility of parole set for Nov. 1, 2048.

December 2015: Netflix releases the series Making a Murderer, in which the filmmakers cast doubt on the legal process used to convict Dassey and Avery. Authorities involved in the case have called the 10-hour series biased, while the filmmakers have stood by their work.

Aug. 12, 2016: A judge throws out Dassey's conviction, ruling that investigators coerced a confession using deceptive tactics. He gives prosecutors 90 days to decide whether to retry Dassey.

Nov. 14, 2016: A judge rules that Dassey should be released while prosecutors appeal the decision that overturned Dassey's conviction.

June 22, 2017: A three-judge federal appeals panel rules that Dassey's confession was improperly obtained and he should be retried or released from prison.