ATMORE, Ala. (AP) — An Alabama man convicted of killing a woman in 1988 was put to death Tuesday evening in the nation’s sixth execution by nitrogen gas. Gregory Hunt was pronounced dead at 6:26 p.m. at a south Alabama prison, authorities said, one of four scheduled this week in the United States.

It was the nation’s sixth execution with nitrogen gas. The execution method involves forcing an inmate to breathe pure nitrogen gas, depriving them of the oxygen needed to stay alive.