Convicted murderer Kenneth Smith, who survived an earlier execution attempt by lethal injection, was killed on Thursday night.

Kenneth Smith, a convicted murderer, is the first person executed by nitrogen gas asphyxiation in the United States.

Officials said Smith, 58, was pronounced dead at 8:25 p.m. Thursday (02:25 GMT Friday) at Holman Correctional Facility in Alabama after inhaling pure nitrogen gas through a face mask to cause oxygen deprivation.

His death marks the first time a new method of execution has been used in the United States since lethal injection, the most commonly used method today, was introduced in 1982.

Alabama called its new protocol “the most painless and humane method of execution known to man.”

The last gas execution in the United States took place in 1999, when a convicted murderer was executed with hydrogen cyanide.

Alabama is one of three U.S. states that have approved its use Nitrogen hypoxia as a method of execution, along with Oklahoma and Mississippi.

United Nations human rights experts and lawyers for Smith, who survived Alabama’s earlier execution attempt by lethal injection, had tried to prevent that by saying that was the method risky and could result in a painful death or non-fatal injury.

According to the Associated Press, Smith’s execution lasted about 22 minutes, and he appeared to shake and writhe on the stretcher for several minutes, sometimes pulling at the shackles. This was followed by several minutes of heavy breathing until breathing could no longer be felt.

In a final statement before his execution, Smith said, “Tonight, Alabama is causing humanity to take a step backwards. … I leave with love, peace and light.”

Alabama Gov. Kay Ivey said the execution was justified for the March 1988 contract killing of 45-year-old Elizabeth Sennett.

“After more than 30 years and attempt after attempt to game the system, Mr. Smith has answered for his terrible crimes. … I pray that Elizabeth Sennett’s family can receive separation after all the years they have struggled with this great loss,” she said in a statement following Smith’s execution.

Sennett was found dead in her home with eight stab wounds to her chest and one on each side of her neck. Smith was one of two men convicted of the murder. The other, John Forrest Parker, was executed in 2010.

Prosecutors said the men were each paid $1,000 to kill Sennett on behalf of her pastor husband, who was deeply in debt and wanted to collect on the insurance. According to court documents, the husband, Charles Sennett Sr., killed himself as the investigation focused on him as a suspect.

Smith’s 1989 conviction was overturned, but he was re-sentenced in 1996. The jury recommended a life sentence 11-1, but a judge overturned that and sentenced him to death.

In Alabama, a judge is no longer allowed to overrule a jury’s death penalty decision.

In 2023, there were 24 executions in the United States, all by lethal injection.