Kenneth Eugene Smith: Alabama carries out first US nitrogen gas execution

Alabama has executed convicted murderer Kenneth Eugene Smith with nitrogen gas, the first time the controversial method has been used in the US.

Smith, 58, lost two final appeals to the Supreme Court and one to a federal appeals court, arguing the execution was a cruel and unusual punishment.

In 2022, Alabama tried and failed to execute Smith by lethal injection.

He was convicted in 1989 of murdering a preacher's wife, Elizabeth Sennett, in a killing-for-hire.

Smith is the first person to be put to death using pure nitrogen gas in the US and, according to the Death Penalty Information Center, anywhere in the world.

Breathing the gas without oxygen causes the cells to break down and leads to death. Alabama said in an earlier court filing that it expected Smith to lose consciousness within seconds and die in a matter of minutes.

But the method was denounced by some medical professionals, who warned it could cause a range of catastrophic mishaps, ranging from violent convulsions to survival in a vegetative state.

Alabama and two other US states have approved the use of nitrogen hypoxia as an alternative method of execution because the drugs used in lethal injections have become more difficult to find, contributing to a fall in the use of the death penalty nationally.

On Thursday, the Alabama Department of Corrections shared details from the inmate's final 48 hours.

Smith was visited by members of his family, two friends, his spiritual adviser and his attorney.

He had a breakfast of two biscuits, eggs, grape jelly, applesauce and orange juice.

His final meal was steak and eggs with hash browns.

Alabama tried to execute Smith by lethal injection two years ago, but they were unable to raise a vein before the state's death warrant expired.

On Thursday night, the Supreme Court denied him a last-minute reprieve.

Three liberal justices dissented from the conservative-led majority's ruling. 

"Having failed to kill Smith on its first attempt, Alabama has selected him as its 'guinea pig' to test a method of execution never tested before," Justice Sonia Sotomayor wrote. "The world is watching."

The Supreme Court declined to intervene in response to another challenge relating to Smith's case on Wednesday night. No justice publicly dissented from that ruling.

This is a developing story. More updates to follow.