ANGOLA, La. (AP) — Louisiana used nitrogen gas to put a man to death Tuesday evening for a killing decades ago, marking the first time the state has used the method as it resumed executions after a 15-year hiatus.

Jessie Hoffman Jr., 46, was pronounced dead at 6:50 p.m. at the Louisiana State Penitentiary, authorities said, adding the nitrogen gas had flowed for 19 minutes during what one official characterized as a “flawless” execution.

Witnesses to the execution said Hoffman appeared to involuntarily shake or had “some convulsive activity.” But the three witnesses who spoke — including two members of the media — agreed that, based on the protocol and what they learned about the execution method, nothing seemed out of the ordinary.

Witness Gina Swanson, a reporter with WDSU, described the execution from her viewpoint as “clinical” and “procedural.” She said there was nothing that occurred during the process that made her think, “Was that right? Was that how it was supposed to go?”

Hoffman declined to make a final statement in the execution chamber. He also declined a final meal.

It was the fifth time nitrogen gas was used in the U.S. after four executions by the same method — all in Alabama. Three other executions, by lethal injection, are scheduled this week — in Arizona on Wednesday and in Florida and Oklahoma on Thursday.

Hoffman was convicted of the murder of Mary “Molly” Elliott, a 28-year-old advertising executive who was killed in New Orleans.

At the time of the crime, Hoffman was 18 and has since spent much of his adult life at the penitentiary.