The U.S. Supreme Court has declined to hear a death row inmate's challenge to Mississippi's method of execution by injection.
The court issued its order without comment Monday.
The 5th U.S. Circuit Court of Appeals last November upheld a Mississippi federal judge's dismissal of a lawsuit filed by Roger E. Thorson against Corrections Commissioner Christopher Epps.
A three-judge panel of the 5th Circuit said most of Thorson's claims about the protocol were speculation.
Thorson was sentenced to death for killing a former girlfriend on the Mississippi Gulf Coast in 1987.
Thorson's case marked the second time the 5th Circuit had considered a challenge to Mississippi's lethal injection protocol.
In 2008, a challenge was brought by Leo Dale Bishop and was rejected. Bishop was executed for his role in a 2000 slaying.