The longest serving death row inmate in the US has been resentenced to life in prison after prosecutors in Texas concluded the 71-year-old man is ineligible for execution and incompetent for retrial due to his long history of mental illness.

The ruling means Raymond Riles is immediately eligible for parole, although prosecutors and the victim’s family have said they will oppose that.

Riles has spent more than 45 years on death row for fatally shooting John Thomas Henry in 1974 at a Houston car lot following a disagreement over a vehicle.

He is the country’s longest serving death row prisoner, according to the Death Penalty Information Centre.

Riles was resentenced on Wednesday (local time) after the Texas Court of Criminal Appeals ruled in April that his “death sentence can no longer stand” because jurors did not properly consider his history of mental illness.

Riles attended his resentencing by Zoom from the Polunsky Unit in Livingston, which houses the state’s death row inmates. He said little during the court hearing.

Riles’ lawyers asked that he appear via Zoom because they were concerned his various health issues, including severe mental illness, heart disease and ongoing recovery from prostate cancer, make him susceptible to contracting COVID-19.

Several members of Mr Henry’s family took part in the virtual court hearing but did not make any statement before state District Judge Ana Martinez resentenced Riles to life in prison.

“We express our condolences to the family of Mr Henry [who] we know have suffered an unimaginable loss. We are profoundly sorry for that,” said Jim Marcus, a professor at the University of Texas at Austin School of Law and one of Riles’ lawyers.

In a statement, Harris County District Attorney Kim Ogg said Riles was incompetent and “therefore can’t be executed.”

During his time on death row, Riles has been treated with heavy antipsychotic medications but was never deemed mentally competent to be executed, according to prosecutors and his lawyers.

He had been scheduled for execution in 1986 but got a stay due to competency issues. While Riles spent more than 45 years on death row in Texas, prisoners in the US typically spend more than a decade awaiting execution, according to the Death Penalty Information Centre.

Judge Martinez was not able to resentence Riles to life in prison without parole because it was not an option under state law at the time of his conviction.

Riles’ new sentence means he is immediately eligible for parole. The Texas Board of Pardons and Paroles will automatically conduct a parole review in his case, Mr Marcus said.

A co-defendant in the case, Herbert Washington, was also sentenced to death, but his sentence was overturned, and he later pleaded guilty to two related charges. He was paroled in 1983.

-AAP