Huntsville, Texas - The US state of Texas on Tuesday executed by lethal injection a man sentenced to death for killing an elderly woman during a carjacking two decades ago, despite efforts by his lawyers to postpone the carrying out of his sentence.

Jedidiah Murphy (48) was declared dead at 10:15 PM local time following his execution at a prison in Huntsville, the Texas Department of Criminal Justice said.

"To the family of the victim I want to say I sincerely apologize for all I did. I hope this brings you closure, thank you," the inmate said as part of his last statement before reciting a psalm.

Murphy, who has spent two decades on death row, was convicted of the October 4, 2000, carjacking and fatal shooting of an elderly woman he forced at gunpoint to give him a ride.

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According to the arguments of his lawyers, reported by the local press in recent weeks, Murphy had been abused as a child in foster homes and showed signs of serious mental illness, including suffering from hallucinations.

Although he did not deny the crime, he claimed his intention was not to kill the woman and he tried in vain to have his sentence modified.

Murphy's lawyers had recently got an appeals court to grant a stay of execution, citing questions about the evidence used in his death sentence.

He denied involvement in two robberies and a kidnapping of which he was also accused.

On Tuesday, the Supreme Court lifted that stay, at the request of the Texas Attorney General's Office.

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His defense had also asked to postpone the execution, alleging that the lethal injection chemicals had been exposed to heat during a fire and could have deteriorated, but that request was rejected Tuesday night, according to the Supreme Court's website.

His death on World Day Against the Death Penalty brings the number of executions in the US this year to 20.