By Jon Herskovitz
AUSTIN, Texas (Reuters) - The U.S. Supreme rejected a last-minute appeal from a Texas inmate about an hour before his planned execution on Thursday for murdering a prison guard in 1999.
The decision cleared the way for Robert Pruett, 38, to be put to death by lethal injection in the state's death chamber in Huntsville at 6 p.m. local time (2300 GMT).
If the execution goes ahead, it would be the 544th in Texas since the U.S. Supreme Court reinstated the death penalty in 1976, the most of any state.
Lawyers for Pruett had argued he was innocent and called on the U.S. high court to spare his life. The decision issued by Justice Samuel Alito did not provide a reason for the court's decision.
Pruett, who had been serving a 99-year sentence as an accessory to a murder committed by his father, was convicted of killing prison guard Daniel Nagle by stabbing him repeatedly with a shank.
Prosecutors said he murdered the corrections officer because Nagle had reprimanded him for carrying a sandwich into the recreation yard. Torn pieces of the disciplinary report on Pruett were found near Nagle's body.
"No witnesses testified they observed the attack, and no physical evidence connected Robert Pruett to the murder," lawyers for the inmate wrote in their petition to the Supreme Court filed on Tuesday.
They said Pruett, who has maintained his innocence, was convicted on the unreliable testimony of prison informants and neither Pruett's fingerprints nor DNA material were found on the torn report. Lawyers have also asked the state to release the shank and Nagle's clothes for DNA testing after inconclusive tests took place in 2000.
In a legal filing with the Supreme Court, the state of Texas said: "Pruett has raised nothing new that casts any doubt on his guilt."
They added he had raised the same concerns before in previous filings and had been rejected.
"His claims are based on pure speculation and do not demonstrate his factual innocence," Texas Attorney General Ken Paxton and others said in the filing submitted to the Supreme Court on Wednesday.
(Reporting by Jon Herskovitz; Editing by Peter Cooney and Jonathan Oatis)