The remorseless final words of inmate Alan Miller who became second US inmate to be killed with nitrogen gas have been released after he died on Thursday.

Miller was pronounced dead at 6:38 p.m. local time at a south Alabama prison. He shook and trembled on the gurney for about two minutes with his body at times pulling against the restraints. That was followed by about six minutes of periodic gasping breaths.

Miller told those witnessing the execution: “I didn’t do anything to be in here,” Miller said in his final words that were at times muffled by the mask that covered his face from forehead to chin.

Ahead of his scheduled execution, Miller was visited by three attorneys, a friend, his brother-in-law, two sisters, a brother and spiritual advisor, but declined to make any phone calls. For his final meal he ate hamburger steak, baked potato and fries.

Miller, a former delivery truck driver, was convicted of the killings of three separate co-workers Lee Holdbrooks, Christopher Scott Yancy and Terry Jarvis on Aug. 5, 1999.

“Tonight, justice was finally served for these three victims through the execution method elected by the inmate, Alabama Gov. Kay Ivey said in a statement. “His acts were not that of insanity, but pure evil. Three families were forever changed by his heinous crimes, and I pray that they can find comfort all these years later.”

Miller had initially pleaded not guilty by reason of insanity but later withdrew the plea. A psychiatrist hired by the defense said that Miller was mentally ill but his condition wasn’t severe enough to use as a basis for an insanity defense, according to court documents. Jurors convicted Miller after 20 minutes of deliberation and recommended by a vote of 10-2 that he receive the death penalty.

Alabama had first attempted to execute Miller by way of lethal injection but technicians were unable to find a suitable vein on the nearly 360 pound inmate. Miller’s attorney’s challenged the use of nitrogen gas as the method of execution citing the previous case of Kenneth Smith who was the first person in the U.S. using the method.

The method involves placing a respirator gas mask over the inmate’s face to replace breathable air with pure nitrogen gas, causing death by lack of oxygen. Alabama officials and advocates have argued over whether Smith suffered an unconstitutional level of pain during his execution after he shook in seizure-like spasms for more than two minutes while strapped to the gurney and then gasped for breath for several minutes.

Miller was one of five exceptions scheduled to take place in the U.S. over a week-long span with executions either already carried or scheduled to take place in the states of South Carolina, Missouri, Alabama, Oklahoma and Texas.