Magistrate Judge William Duffin said in Friday’s ruling that investigators made false promises to Dassey by assuring him ‘‘he had nothing to worry about.’’

The U.S. District Court in Milwaukee overturned Brendan Dassey’s conviction and ordered him freed within 90 days unless prosecutors decide to retry him. A spokeswoman for the state Department of Justice, which was handling the case, did not immediately return a message seeking comment.

MADISON, Wis. (AP) — A federal court in Wisconsin on Friday overturned the conviction of a man found guilty of helping his uncle kill Teresa Halbach in a case profiled in the Netflix documentary ‘‘Making a Murderer.’’


‘‘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 Fourteenth Amendments,’’ Duffin wrote. The ruling comes after Dassey’s appeal was rejected by state courts.

Dassey confessed to helping his uncle Steven Avery carry out the rape and murder of Halbach, but attorneys argued that his constitutional rights were violated throughout the investigation.

Dassey was 16 when Halbach was killed in 2005 after she went to the Avery family auto salvage yard to photograph some vehicles.

Avery was tried and convicted separately in the homicide. Both Avery and Dassey are serving separate life sentences.

Dassey’s case burst into the public’s consciousness with the popularity of the ‘‘Making a Murderer’’ documentary that debuted in December.

Attorneys for Dassey did not immediately return messages seeking comment.

The filmmakers behind ‘‘Making a Murderer’’ cast doubt on the legal process used to convict Avery and Dassey, and their work has sparked national interest and conjecture. Armchair investigators have flooded Twitter and message boards, and key players in the case have appeared on national news and talk shows.


Authorities involved in the case have called the 10-hour series biased, while the filmmakers have stood by their work.