A judge has overturned the conviction of a Missouri woman who was a psychopath when she pleaded guilty to a 1980 murder that her lawyers argue was actually committed by a disgraced police officer.

Judge Ryan Horsman ruled late Friday that Sandra Hamm, who has spent 43 years in prison, has presented evidence of her actual innocence and should be released within 30 days unless prosecutors try her again. He said her trial attorneys were ineffective and prosecutors failed to present evidence that could have helped her.

Her lawyers say this is the longest time a woman has been kept in prison for wrongful conviction. They filed a petition demanding her immediate release.

“We are grateful to the court for recognizing the grave injustice that Ms. Hemme has suffered for more than four decades,” her lawyers said in a statement. They vowed to continue their efforts to dismiss the charges and reunite Hemme with her family.

A spokesman for Missouri Attorney General Andrew Bailey did not immediately respond to a text or email message seeking comment Saturday.

When Hemme was first questioned about the death of 31-year-old library worker Patricia Jeschke, she was shackled with leather wrists and was so sedated that she “was unable to keep her head straight” or “provide anything articulate beyond one-word answers,” according to her lawyers from the New York-based Innocence Project.

They alleged in a petition seeking Hemme’s exoneration that officers ignored Hemme’s “wildly contradictory” statements and suppressed evidence that incriminated Michael Holman, a then-police officer who tried to use the dead woman’s credit card.

The judge wrote that “other than Ms. Hemme’s unreliable statements, no evidence links her to the crime.”

“On the contrary, this court finds that the evidence directly links Holman to this crime and the murder scene,” he said.

It began on November 13, 1980, when Jeske disappeared from work. Her worried mother peered through her apartment window and found her daughter’s naked body lying on the floor in a pool of blood. Her hands were tied behind her back with a telephone cord and a piece of pantyhose was wrapped around her neck. A knife was held beneath her head.

The brutal killing made headlines, with detectives working 12-hour days to solve it. But Hemme wasn’t on their radar until she showed up nearly two weeks later at the home of a nurse who had once treated her, wielding a knife and refusing to leave.

Police found him in a closet, and took him back to St. Joseph’s Hospital, the latest in a series of hospitalizations since he began hearing voices at age 12.

Jeschke had been discharged from the same hospital the day before her body was found, and had arrived at her parents’ home that night after traveling more than 100 miles (160 km) across the state.

Law enforcement agencies found the timing suspicious. At the time the interrogation began, Heme was being given antipsychotic medication, which caused involuntary muscle spasms. She complained that her eyes were rolling back, the petition said.

Detectives found that Hemme appeared “mentally confused” and was not able to fully understand their questions.

“Each time police took a statement from Ms. Hemme, it changed dramatically from the previous statement, often incorporating clarifications of facts police had recently uncovered,” her attorneys wrote.

Ultimately, he claimed he had seen a man named Joseph Wabski murder Jeschke.

Wabski, whom he met when they both stayed in the state hospital’s detoxification unit at the same time, was charged with murder. But prosecutors quickly dropped the case after discovering he was in an alcohol treatment center in Topeka, Kansas at the time.

Upon learning that he could not be the killer, Hemme cried, and said that he alone was the killer.

But police also began looking for another suspect—one of their own. About a month after the murder, Holman was arrested for falsely reporting that his pickup truck had been stolen and receiving insurance payments. It was the same truck seen near the crime scene, and the officer’s claim that he had spent the night with a woman at a nearby motel could not be confirmed.

In addition, she had tried to use Jeschke’s credit card at a camera store in Kansas City, Missouri, the same day her body was found. Holman, who was eventually fired from his job and died in 2015, said he found the card in a purse that had been thrown in a ditch.

During a search of Holman’s home police found a pair of horseshoe-shaped gold earrings in a cupboard, as well as jewellery stolen from another woman during a burglary earlier that year.

Jeschke’s father said he recognized the earrings as ones he had bought for his daughter. But then Holman’s four-day investigation ended abruptly, many of the details that emerged were never given to Hemme’s lawyers.

Meanwhile, Hemme was growing desperate. She wrote to her parents on Christmas Day 1980, “Even though I’m innocent, they want to put someone in jail so they can say the case is solved.” She said she might change her plea to guilty.

“Just let it be over,” she said. “I’m tired.”

And that’s exactly what she did the following spring, when she agreed to plead guilty to a death sentence in exchange for an abatement of the capital punishment provision.

Even that was a challenge; the judge initially rejected her guilty plea because she couldn’t share enough details about the incident, saying: “I actually didn’t know I did it until it was in the newspapers and on the news three days later.”

His lawyer told him his only chance of avoiding the death penalty was if the judge accepted his guilty plea. After a break and some coaching, he provided more information.

That plea was later rejected on appeal. But he was convicted again in 1985 after a one-day trial in which jurors were not told what his current lawyers called “excessively forceful” interrogation.

Larry Herman, who helped get Hemme’s initial guilty plea dismissed and later became a judge, said in the petition that he believed Hemme was innocent.

“The system failed them at every opportunity,” he said.