Thomas Bartlett “Bart” Whitaker, 38, had been one of three men awaiting execution Thursday in three different US states.

“Mr Whitaker must spend the remainder of his life behind bars as punishment for this heinous crime,” Abbott wrote in a proclamation explaining his decision, shortly before the scheduled execution.

Abbott said he had taken into consideration the fact that “the person who fired the gun that killed the victims did not receive the death penalty, but Mr Whitaker, who did not fire the gun, did get the death penalty.”

He added: “Mr Whitaker’s father, who survived the attempt on his life, passionately opposes the execution of his son. Mr Whitaker’s father insists that he would be victimized again if the state put to death his last remaining immediate family member.

“Also, Mr Whitaker voluntarily and forever waived any and all claims to parole in exchange for a commutation of his sentence from death to life without the possibility of parole.”

The Texas Board of Pardons and Paroles also voted unanimously for the pardon.

Whitaker was convicted of hiring a hitman in 2003 to kill his father, mother, and brother. The gunman also shot him in the arm to provide a cover story for the family slaying. Police said the son had developed a hatred for his family and hoped to inherit around $1 million (RM3.9 million) on their deaths.