A South Korean man who has spent 24 years in prison for setting a fire in Pennsylvania that killed his daughter took a big step toward freedom Friday when a federal judge threw out his murder conviction, ruling it was based on now-discredited arson science.

U.S. District Judge William Nealon vacated Han Tak Lee’s state conviction and life-without-parole sentence, ordering that Lee either be tried again within 120 days or released from prison.

Lee’s attorney said he will try to get bail for his elderly client next week. Monroe County District Attorney E. David Christine Jr., who prosecuted Lee in 1990, said he will “very likely” appeal the ruling to the Philadelphia-based 3rd U.S. Circuit Court of Appeals.

Lee, a clothing store owner in New York City, had taken his volatile, mentally ill daughter to a religious retreat in the Pocono Mountains at the suggestion of the family pastor. Early on July 29, 1989, the cabin they shared became engulfed in flames. Lee escaped, but 20-year-old old Ji Yun Lee’s body was found in the ashes, curled in the fetal position.

Lee has long argued the fire was accidental, and in 2012, the 3rd Circuit granted his request for an independent examination of evidence. That review, completed in June by a magistrate judge, concluded that “much of what was presented to Lee’s jury as science is now conceded to be little more than superstition.”

At the time of his trial, investigators were taught that unusually hot and intense fires indicated the use of an accelerant and that arson could be confirmed by the presence of deep charring or shiny blistering of wood as well as “crazed glass,” tiny fractures in windows. Research has since debunked these and other notions about arson.

Lee’s case is one of dozens around the country to come under scrutiny because of outdated beliefs about how arson can be detected.

Christine said it’s too early to say whether he will retry Lee if the 3rd Circuit rejects his probable appeal.

“I’d originally said it would be close to impossible because of the passage of time, but quite frankly, that decision should await a careful review of how many witnesses are still alive, where are they located, how much do they remember,” Christine said. “There’s no question it would be very difficult.”

He said he continues to believe the jury got it right.

Defense attorney Peter Goldberger, who has worked on Lee’s case for 12 years, said he sees no basis for an appeal and that it would be “impossible to try him fairly and ethically.”

“We’re very confident that this is the end,” he said. “The time for delay is over in this case.”