The U.S. Supreme Court has refused to block Tuesday's scheduled execution of an inmate convicted of fatally stabbing a prison guard while already on Florida's death row.

Askari Abdullah Muhammad, previously known as Thomas Knight, was set to die by lethal injection Tuesday evening.

The 62-year-old Muhammad was first condemned to die for the 1974 abduction and killings of Sydney and Lillian Gans, a Miami couple. He was sentenced to die again for killing corrections officer Richard Burke in 1980 using a sharpened spoon.

His execution has been delayed for so long because of numerous appeals and rulings, including a 1987 federal appeals court tossing out his death sentence because he hadn't been allowed to put character and background witnesses on the stand during the penalty phase.