Washington DC - The US Supreme Court hears the high-profile case on Wednesday of an Oklahoma man whose conviction and death sentence have sparked appeals for clemency from Pope Francis and Hollywood stars.

Richard Glossip (61) was convicted – twice – of the 1997 murder of Barry Van Treese, an Oklahoma City motel owner, and sentenced to death.

Execution dates have been scheduled nine times and he has eaten three "last meals."

Glossip's first conviction, in 1998, was overturned because of ineffective counsel, but he was tried once more in 2004 and again found guilty. Since then, his case has been subject to an extraordinary series of twists and turns.

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The Republican attorney general of Oklahoma – generally an ardent supporter of the death penalty – is among those seeking a new trial for Glossip. Citing "grave prosecutorial misconduct" and a star witness who lied on the stand, Oklahoma Attorney General Gentner Drummond asked the Oklahoma Court of Criminal Appeals last year to vacate Glossip's conviction.

The Oklahoma court refused and Glossip was scheduled to be executed by lethal injection on May 18, 2023.

The Supreme Court stayed his execution, however, following an appeal by Drummond and Glossip's lawyers and agreed in January to hear the case. An independent attorney has been appointed by the Supreme Court to defend the Oklahoma court's refusal to vacate Glossip's conviction.

David Cole, legal director of the American Civil Liberties Union, noted the unusual nature of the proceedings.

"It's a remarkable case in which both the defense and the prosecution believe this man should not be executed and yet they have to come to the Supreme Court to seek that relief," Cole said.

"And the Supreme Court has had to appoint counsel to argue that he should be executed – notwithstanding the desires of the person who prosecuted him and the individual who stands to lose his life."

Glossip has steadfastly maintained his innocence in the murder of Van Treese, owner of the Best Budget Inn.

Glossip, who managed the motel, was found guilty of hiring another motel employee, maintenance man Justin Sneed, to carry out the actual murder.

Sneed, who was 19 at the time, confessed to bludgeoning Van Treese to death with a baseball bat but escaped a death sentence with his testimony that Glossip had masterminded the plot and paid him to carry out the murder.

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Glossip was convicted solely on the testimony of Sneed.

An independent investigation commissioned by the attorney general found that Sneed lied on the stand and that prosecutors had "knowingly elicited his false testimony" while covering up evidence of his mental illness.

Actors Mark Ruffalo and Susan Sarandon and British billionaire Richard Branson have been among the celebrities advocating in the past for Glossip's life to be spared.

In 2015, when Glossip's execution appeared imminent, the representative of Pope Francis in the US sent a letter on behalf of the pontiff to the then governor of Oklahoma asking that the execution be called off.

His case has also been the subject of a four-episode documentary titled Killing Richard Glossip.

There have been three executions in Oklahoma this year and a total of 19 in the US.