Image copyright AP Image caption Brendan Dassey (right) was sentenced to life in prison

A US federal judge has overturned the murder conviction of Brendan Dassey, whose case was examined in Netflix's popular Making a Murderer documentary.

Dassey, 26, will be released within 90 days, unless the state decides to retry him or there is an appeal.

Dassey, who has learning difficulties, and his uncle Steven Avery were convicted of murdering a young woman, Teresa Halbach, in 2005.

Avery and Dassey, who was 16 at the time, were sentenced to life in prison.

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On Friday, Judge William Duffin stated in the court ruling that investigators in the 2007 trial made false promises to Dassey by assuring him "he had nothing to worry about".

"These repeated false promises, 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 under the Fifth and 14th Amendments," the judge said.

The Fifth Amendment of the US Constitution guarantees the right to a fair trial, including the right to silence. The 14th Amendment guarantees equal treatment before the law.

Image copyright Netflix Image caption The case of Steven Avery (pictured) and Brendan Dassey received wide attention after the release of the documentary in 2015

The verdict comes after Dassey's appeal was rejected by state courts.

Steven Drizin, Professor of law at Northwestern University, became involved in the push to have the conviction overturned.

"I thought that this was a confession that was the result of police coercion," he told the BBC's Today programme.

"These detectives had taken advantage of a young man who had severe learning difficulties. The only facts in the confession had been fed to him by the investigators."

The case received wide attention in the US and across the world after the release of the 10-part documentary Making a Murderer in December 2015.

The filmmakers cast doubt on the legal process to convict Dassey and Avery.

The documentary tells the real-life story of Avery, who was wrongfully imprisoned for 18 years for sexual assault.

After his release, he was accused and found guilty of murdering Teresa Halbach, a photographer for Auto Trader Magazine.

Ms Halbach's charred remains were found at Avery's car salvage yard a week after she had gone there to photograph a minivan for sale.

The series focused on the conduct of law officials in Manitowoc County, Wisconsin, who risked a huge financial penalty over the first case.