OKLAHOMA CITY (AP) — An Oklahoma judge has exonerated a man who spent nearly 50 years in prison for murder, the longest serving inmate to be declared innocent of a crime.

Glynn Simmons, 71, who was released in July after prosecutors agreed that key evidence in his case was not turned over to his defence lawyers, was ruled innocent Tuesday.

“This court finds by clear and convincing evidence that the offense for which Mr Simmons was convicted, sentenced and imprisoned… was not committed by Mr Simmons,” according to the ruling by Oklahoma County District Judge Amy Palumbo.

Simmons served 48 years, one month and 18 days since his conviction, making him the longest imprisoned US inmate to be exonerated, according to data kept by The National Registry of Exonerations.

Simmons said afterward that he feels vindicated after his time in prison that included initially being sentenced to death row.

“It’s a lesson in resilience and tenacity,” Simmons said during a brief news conference following the ruling. “Don’t let nobody tell you that it (exoneration) can’t happen, because it really can.”

Simmons has maintained his innocence, saying he was in Louisiana at the time of the 1974 slaying of Carolyn Sue Rogers inside an Edmond liquor store.

He and co-defendant Don Roberts were both convicted in 1975 of the murder and initially sentenced to death. Their sentences were reduced to life in prison in 1977 after US Supreme Court rulings related to capital punishment. Roberts was released on parole in 2008.

Palumbo in July ordered a new trial for Simmons after District Attorney Vicki Behenna said prosecutors had failed to turn over evidence in the case, including a police report that showed an eyewitness might have identified other suspects in the case.

Behenna in September said there is no longer physical evidence in the case against Simmons and announced she would not retry him, though she opposed declaring him actually innocent.

A spokesperson for Behenna declined immediate comment on Wednesday.

The ruling makes Simmons eligible for up to $175,000 in compensation from the state for wrongful conviction and opens the door for a federal lawsuit against Oklahoma City and law enforcement involved in Simmons’ arrest and conviction, defence attorney Joe Norwood said Wednesday.

Compensation, though, is likely years away, Norwood said and Simmons is currently living on donations while undergoing treatment for cancer that was detected after his release from prison.

“Glynn is having to live off of GoFundMe, that’s literally how the man is surviving right now, paying rent, buying food,” Norwood said. “Getting him compensation, and getting compensation is not for sure, is in the future and he has to sustain himself now.”