Texas has executed a man convicted of murdering a prison guard in 1999, after the US Supreme Court rejected a last-minute appeal to spare his life despite arguments by his lawyers that he was innocent.
Robert Pruett, 38, was put to death by lethal injection at the state's death chamber in Huntsville and pronounced dead at 6.46pm local time, the Texas Department of Criminal Justice said.
He was the 544th person executed in Texas since the US Supreme Court reinstated the death penalty in 1976, the most of any state. It was Texas' sixth execution this year.
About an hour before the scheduled execution, the Supreme Court said it rejected Pruett's petition. The decision issued by Justice Samuel Alito did not provide a reason.
Pruett, sent to prison as a teenager and 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 officer because Mr Nagle had reprimanded him for carrying a sandwich into the recreation yard. Torn pieces of the disciplinary report on Pruett were found near the officer'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 last 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 had 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."