In a first, United States executed a convicted murder using nitrogen gas on Thursday in the state of Alabama.

Accordinfg to the state of Alabama it was “the most painless and humane method of execution known to man.”

The execution took place a fter a elengthy legal battle, after the convict, Kenneth Smith, appealed saying that the method was dangerous and could lead to non-fatal injury.

Smith, convicted of a 1988 murder-for-hire, was a rare prisoner who had already survived one execution attempt. In November 2022, Alabama officials aborted his execution by lethal injection after struggling for hours to insert an intravenous line’s needle in his body.

In Smith’s second and final trip to the execution chamber on Thursday, executioners restrained him in a gurney and strapped a commercial industrial-safety respirator mask to his face. A canister of pure nitrogen was attached to the mask that once flowing, deprived him of oxygen.

The execution began at 7:53 p.m. (0153 GMT Friday) and Smith was declared dead at 8:25 p.m. (0225 GMT), prison officials said.

Smith appeared to remain conscious for several minutes after the nitrogen was activated, according to five journalists were allowed to watch the execution through glass as media witnesses. He then began shaking and writhing on the gurney for about two minutes, and then could be seen breathing deeply for several minutes before his breathing slowed and became imperceptible, the witnesses said.

Alabama officials had said in court filings they expected Smith would be rendered unconscious in under a minute and die shortly after.

“It appeared that Smith was holding his breath as long as he could,” Alabama Corrections Commissioner John Hamm said when asked at a press conference if the writhing had been expected. “He struggled against the restraints a little bit but it’s an involuntary movement and some agonal breathing. So that was all expected.”

Before the nitrogen was switched on, Smith made a lengthy final statement that began: “Tonight, Alabama caused humanity to take a step backward.”

His wife and other relatives attended and he gestured towards them. “I’m leaving with love, peace and light,” he said, according to media witnesses. “Love all of you.”