The United States executed a man who killed a motorist that came to his help on a highway, after the Supreme Court rejected a last-minute appeal.
Allen Nicklasson, 41, was given the lethal injection late Wednesday in Bonne Terre, Missouri, local media said.
He had turned to the Supreme Court arguing that the lethal injection of pentobarbital was "cruel and unusual punishment" contrary to his constitutional rights.
Nicklasson had unsuccessfully argued that the use of pentobarbital was unconstitutional because the compounding pharmacy that made it had not been approved by medical authorities.
He was put to death by a single injection of a lethal dose of the drug, according to a statement by prison authorities.
Several US states have resorted to the use of pentobarbital in the face of a shortage of barbiturates.
It was the 38th execution this year in the United States, according to the Death Penalty Information Center.
Two of Nicklasson's accomplices were also convicted.