The execution is the 22nd in the U.S. this year and the sixth in Alabama, which has put three of the men to death using nitrogen gas.

An Alabama prisoner convicted of the 1994 murder of a female hitchhiker became the third person executed by nitrogen gas in both the U.S. and Alabama.

Carey Dale Grayson, 50, fought his restraints and raised both middle fingers just before gas was administered, a witness said.