Three months after overturning his conviction, a Wisconsin judge on Monday ordered that Brendan Dassey, one of the subjects in Netflix’s documentary series Making a Murderer, be released from prison, under supervision.

The order by US magistrate Judge William Duffin was immediately challenged by Wisconsin’s attorney general, Brad Schimel, whose office announced it would file an emergency motion to stay the decision.

Duffin cast doubt in his ruling on the state’s chances of success in appealing against his earlier decision to overturn Dassey’s conviction and said there was “no indication” that Dassey “has the inclination much less the means to flee”.

“Dassey has offered a detailed release plan that was prepared with the assistance of a clinical social worker with experience in similar cases,” the judge wrote. “That social worker would remain involved in assisting Dassey as he adjusts to freedom following his decade in prison.”

Dassey, 27, has been incarcerated since 2007 over the murder of Teresa Halbach, a local photographer. Dassey and his uncle, Steven Avery, were found guilty in Halbach’s 2005 death in separate trials.

In his August decision to overturn Dassey’s conviction, Duffin called the conduct of the then teenager’s attorney “indefensible”. The attorney, Len Kachinsky, initially represented Dassey before being removed from the case before trial. In his first three weeks representing Dassey, Duffin wrote, Kachinsky spent 10 hours speaking to reporters and only one hour with the teen.

The judge also took aim at investigators who, he said, elicited an “involuntary” confession from Dassey, who was 16 at the time of Halbach’s murder. Dassey’s attorney told the Guardian last year that his remarks to police “fit the profile of a [false] confession to an absolute T”. The officers, for example, suggested he would receive leniency for complying and fed facts “to get Brendan to say how Ms Halbach died”, said the attorney, Laura Nirider.

Duffin agreed.

“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,” Duffin wrote in his 91-page ruling.

The story drew notoriety for Avery’s connection. Before his arrest over Halbach’s murder, he was seen as the face of a US judicial system that can unfairly convict someone: for 18 years, Avery was jailed for a rape he didn’t commit. Eventually, he was exonerated through DNA evidence.

In the order issued on Monday, Duffin outlined numerous conditions to be imposed on Dassey upon his release and pending the effort by Wisconsin’s attorney general to appeal against the judge’s decision to overturn his conviction. Avery’s appeal remains pending.

Dassey will be supervised by the US probation office in Wisconsin, Duffin ruled, saying it has “experts in addressing issues that Dassey is likely to face upon being released after more than a decade in prison”.

Duffin also said that Dassey cannot contact Avery or any family members of Halbach. If Dassey violates any terms of the order, the judge said, he may be returned to custody pending the outcome of the prosecution’s appeal.

