Bobby Moore, 60, was sentenced to death in 1980 for killing a supermarket worker in a robbery in Houston.

He has since twice avoided the death chamber after rulings that his execution would amount to cruel and unusual punishment, which the Eighth Amendment prohibits.

In 2017, the Supreme Court found that the standards for determining eligibility for execution were “not aligned with the medical community’s information”.

Those standards were in part derived from a Texas appeal court’s ruling in 2004 that became known as the Lennie standard, after the character in John Steinbeck’s Of Mice and Men.

Judge Cathy Cochran said most Texans would not think that Lennie should be executed.

A Texan court re-sentenced Mr Moore, an African-American, in November, making him eligible for parole. State legislators wrote to the parole board in March to say Mr Moore should have been eligible for parole two decades ago. A date for his release has yet to be set.