A man was put to death by lethal injection Thursday in the US state of Oklahoma, officials said, and Alabama carried out an execution with nitrogen gas, the second time such a method has been used in the United States.
The two killings bring the total number of executions this year in the United States to 18, including five in the past week.
Emmanuel Littlejohn, 52, was executed by lethal injection in Oklahoma for the murder of 31-year-old Kenneth Meers during a convenience store robbery in 1992.
While admitting he was present at the scene, he has always denied being the one who shot Meers.
Both he and his accomplice Glenn Bethany blamed each other for the killing.
The two men were convicted of murder but Bethany received life imprisonment, whereas Littlejohn was sentenced to death.
In August, the State Board of Pardons recommended a commutation of Littlejohn's sentence, despite opposition from some of the victim's family.
Speaking on Wednesday to NPR, Littlejohn exhorted Oklahoma Governor Kevin Stitt to intervene.
"Governor, don't kill me for the heck of it," Littlejohn said.
Stitt, a Republican who had only exercised his clemency power once, ultimately denied the request.
Oklahoma Attorney General Gentner Drummond said Thursday that "justice has been served for the murder of Kenny Meers."
- Nitrogen gas controversy -
In Alabama, Alan Miller was put to death over a 1999 workplace shooting spree that killed three colleagues: Lee Holdbrooks, Christopher Scott Yancy and Terry Lee Jarvis.
Miller, 59, was executed at the Atmore penitentiary by pumping nitrogen gas into a facemask, causing him to suffocate.
The method was controversially used by Alabama for the first time in January, despite being compared by the United Nations to a form of torture.
Miller struggled against the restraints on the gurney as he suffocated, shaking and trembling for two minutes, local media reported.
His movements were similar to, but reportedly not as violent as, the first time nitrogen hypoxia was used, local media said.
During the previous such execution, 58-year-old Kenneth Smith reportedly thrashed about for several minutes.
State officials later attributed the convulsions to Smith attempting to hold his breath.
The White House, under Democratic President Joe Biden, said it was "deeply troubled" by Alabama's use of nitrogen in January.
It also drew rebukes from civil liberties groups, the European Union and the UN human rights office.
Alabama Governor Kay Ivey, a Republican, had announced in advance that she would not exercise her clemency power for Miller.
A previous attempt to execute Miller by lethal injection in September 2022 was called off at the last minute due to difficulties inserting the intravenous tube and administering the lethal chemicals in the allotted time.
The death penalty has been abolished in 23 of the 50 US states. Six others (Arizona, California, Ohio, Oregon, Pennsylvania and Tennessee) observe a moratorium on executions by decision of the governor.