Making A Murderer's Brendan Dassey who last month had his murder conviction overturned, may not be released from prison after all.

The 26-year-old was due to leave within 90 days, but the Wisconsin Department of Justice has filed to overturn that.

Prosecutors believe Dassey shouldn't be let out over claims from the defence that there were problems with the investigation.

Attorney General, Brad Schimel, has criticised the judge's decision.

"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," he said.

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

Dassey, who has learning difficulties, and his uncle Steven Avery were convicted of murdering 25-year-old Teresa Halbach, in 2005.

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

His defence argued that he was coerced into confessing to the crime while being interviewed alone and without a lawyer.

But Attorney General, Brad Schimel, believes police were right to carry out the investigation as they did.

"The investigators did not use constitutionally impermissible tactics," he says.

"Two state courts carefully examined the evidence and properly concluded that Brendan Dassey's confession to sexually assaulting and murdering Teresa Halbach with his uncle, Steven Avery, was voluntary."

Responding to the appeal, Brendan Dassey's family and lawyer released a statement, saying: "We are disappointed in the State's decision to prolong Brendan's case by seeking an appeal.

"We look forward to continuing to defend his rights in court. Like Brendan, we remain grateful to his many supporters for their continued loyalty and strength."

His attorney Kathleen Zellner tweeted criticising the announcement in Dassey's case.

The case became well known around the world because of the Making a Murderer series released in December 2015.

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

It tells the real-life story of Avery, who was previously 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.

Her burnt remains were found at Mr Avery's car salvage yard a week after she had visited to take pictures of a van for sale.

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