NEW YORK — An Oklahoma judge has exonerated a man who was in prison for almost half a century for a 1974 murder, the longest wrongful sentence to be served in the US.

Glynn Simmons, 70, was freed in July when a judge ordered a new trial.

But a county district attorney said on Monday there was not enough evidence to warrant one.

In an order on Tuesday, Oklahoma County District Judge Amy Palumbo declared Simmons innocent.

"This court finds by clear and convincing evidence that the offence for which Simmons was convicted, sentenced and imprisoned... was not committed by Simmons," she said in a ruling.

"It's a lesson in resilience and tenacity," Simmons told reporters after the decision, according to the Associated Press. "Don't let nobody tell you that it can't happen, because it really can."

Simmons had served 48 years, one month and 18 days in prison for the murder of Carolyn Sue Rogers during a liquor store robbery in an Oklahoma City suburb. That makes him the longest-serving inmate to be cleared, according to the National Registry of Exonerations.

Simmons was 22 years old when he and a co-defendant, Don Roberts, were convicted and sentenced to death in 1975.

The punishments were later reduced to life in prison because of US Supreme Court rulings on the death penalty.

Simmons had said he was in his home state of Louisiana at the time of the murder.

A district court vacated his sentence in July after finding that prosecutors had not turned over all evidence to defence lawyers, including that a witness had identified other suspects.

Simmons and Roberts were convicted in part because of testimony from a teenager who had been shot in the back of the head. The teenager pointed to several other men during police line-ups.

Roberts was released on parole in 2008.

Wrongfully convicted people who serve time in Oklahoma are eligible for up to $175,000 (£138,000) in compensation.

Simmons is currently battling liver cancer, according to his GoFundMe, which has raised thousands of dollars to help support his living costs and chemotherapy. — BBC