Ernest Johnson, 55, was scheduled to die by lethal injection at the state prison in Bonne Terre, Missouri. The US Supreme Court on Tuesday rejected a separate motion to halt the execution.
Johnson was convicted of bludgeoning to death Mary Bratcher, Mabel Scrubbs and Fred Jones using a hammer, a screw driver and a gun, according to court records. Defense attorneys have argued in unsuccessful appeals that he has an intellectual disability and is not therefore eligible for execution.
A total of 25 people have been executed in the United States so far this year, according to the Death Penalty Information Center, including six in Missouri.
