A Missouri woman who was imprisoned for more than 40 years for murder has had her conviction overturned after a judge found “clear and convincing” evidence that she was innocent of the killing in question. Sandra “Sandy” Hemme, 63, was convicted of – and sentenced to life imprisonment for – the 1980 slaying of Patricia Jeschke, a library worker in St Joseph, Missouri, after Hemme made statements to the police incriminating herself while she was a psychiatric patient. On Friday, Livingston county circuit judge Ryan Horsman ruled that “evidence directly” ties the killing of Jeschke to a local police officer who later went to prison for another crime and has since died. Hemme, who has spent the last 43 years behind bars, must be freed within 30 days unless prosecutors decide to re-try her, the judge said. The ruling came after an evidentiary hearing in January where Hemme’s legal team presented arguments supporting her evidence. Hemme’s prison term marks the longest-known wrongful conviction of a woman in US history, her attorneys with the Innocence Project – a criminal justice nonprofit – said. “We are grateful to the Court for acknowledging the grave injustice Ms Hemme has endured for more than four decades,” her attorneys said in a statement. Hemme initially pleaded guilty to capital murder in exchange for avoiding the death penalty. But her conviction was thrown out on appeal, according to the Associated Press. She was convicted again in 1985 after a one-day trial in which the only evidence against her was her “confession”. In a 147-page petition seeking her exoneration, attorneys argued that authorities ignored Hemme’s “wildly contradictory” and “factually impossible” statements while she was a patient at a psychiatric hospital. Hemme, then 20, was receiving treatment for auditory hallucinations, de-realization and drug use when she was targeted by the police, her attorneys said. She had spent most of her life, beginning from the age of 12, in inpatient psychiatric treatment. Over a series of hours-long interviews, Hemme gave conflicting statements about the murder while being treated with antipsychotic drugs, her attorneys said. “At some points, she was so heavily medicated that she was unable to even hold her head up and was restrained and strapped to a chair,” they wrote. Detectives noted that Hemme seemed “mentally confused” and not able to fully comprehend their questions. Steven Fueston, a retired St Joseph police department detective, testified that he stopped one of the interviews because “she didn’t seem totally coherent”. Police “exploited her mental illness and coerced her into making false statements while she was sedated and being treated with antipsychotic medication”, Hemme’s lawyers said. They alleged that authorities at the time suppressed evidence that implicated Michael Holman, then a 22-year-old police officer who had tried to use the victim’s credit card. Holman’s truck was spotted near the crime scene and a pair of earrings identified by Jeschke’s father were found in Holman’s possession. Holman had been a suspect and was questioned at the time. Many of the details uncovered during the investigation into Holman were never given to Hemme’s attorneys. Holman was investigated for insurance fraud and burglaries and spent time in prison. He died in 2015. In his ruling Friday, Horsman wrote that “no evidence whatsoever outside of Ms Hemme’s unreliable statements connects her to the crime”, adding that those statements had been “taken while she was in psychiatric crisis and physical pain”. In contrast, “this court finds that the evidence directly ties Holman to this crime and murder scene”, Horsman wrote. He said prosecutors had failed to disclose evidence that would have helped Hemme’s defense and that her trial counsel had fallen “below professional standards”. The Missouri attorney general’s office, which fought to uphold her conviction, did not immediately comment on the judge’s ruling, the Kansas City Star reported.