The U.S. Supreme Court declined Thursday night to intervene in Alabama's second attempt to execute an inmate who previously survived a botched lethal injection, with the court's three liberal justices saying they would have heard the man's claims that he was being subjected to cruel and unusual punishment.

In a 6-3 decision, the justices denied Kenneth Eugene Smith's most recent application for a stay of execution and a related petition for review, and Smith was put to death later Thursday night.

Smith's petition argued that an Eleventh Circuit panel wrongly deprived him of a chance to claim that Alabama's novel use of nitrogen gas violated the Eighth Amendment. The appellate court on Wednesday upheld an Alabama federal judge's refusal to issue a preliminary injunction that would have allowed Smith to scrutinize the state's new execution method.

The nation's high court denied an earlier version of Smith's stay application and petition for review on Wednesday without any noted dissents. But this time, Justices Sonia Sotomayor, Elena Kagan and Ketanji Brown Jackson all expressed dismay with the majority's decision.

"With deep sadness, but commitment to the Eighth Amendment's protection against cruel and unusual punishment, I respectfully dissent," Justice Sotomayor wrote in a solo opinion.

The court's majority did not explain its decision.

Smith, 58, was convicted of the 1988 murder-for-hire of Elizabeth Sennett by an Alabama jury in 1996. While the jury recommended 11-1 that Smith should receive a sentence of life in prison, the presiding trial judge overrode the jury's vote and sentenced Smith to death, according to court documents.

Alabama first attempted to kill Smith via lethal injection in November 2022. Alabama Department of Corrections officials spent almost two hours trying to insert an IV to administer the lethal drug, but they failed. According to court documents, the procedure should only take up to six minutes, or 30 minutes in extreme cases.

For nearly two hours, Smith claims, he was jabbed repeatedly with needles and ignored when he complained that the needles were penetrating his muscles and causing severe pain. Officials also tried to insert the IV through his neck at one point, but could not.

Under Alabama's recently adopted nitrogen hypoxia procedure, of which the published details are highly redacted, Smith was to have been fitted with a mask attached to a supply of pure nitrogen. No state had carried out an execution using this method, and the United Nations has condemned it as inhumane and experimental.

"Smith … will be strapped to a gurney," Justice Sotomayor wrote in her dissent Thursday. "He will wear a nitrogen-supplying, off-the-rack mask for which the state has not fitted him or even tried on him. Once the nitrogen is flowing into the mask, his executioners will not intervene and will not remove the mask, even if Smith vomits into it and chokes on his own vomit."

Smith has warned about the unknown risks involved with this method of execution in various court filings and hearings, and Justices Sotomayor, Kagan and Jackson said he should be allowed to fully investigate them.

He raised concerns about Alabama's lethal injection procedures ahead of his November 2022 execution attempt as well, Justice Sotomayor wrote, but the court ignored him. He shortly thereafter became the third inmate to experience difficulties with insertion of the IV and the second to survive a botched lethal injection execution.

"I sincerely hope that he is not proven correct a second time," she wrote.

Justice Kagan wrote separately, and was joined by Justice Jackson, to add that she would grant Smith's petition for review to consider whether Alabama's use of nitrogen gas would hold up under the "extremely demanding standard" the Supreme Court established in its 2015 decision in Glossip v. Gross, which held that a prisoner must show that serious pain is "sure or very likely" to occur in order to challenge an execution method under the Eighth Amendment.

"Arguably, that standard can work fairly only when more is capable of being known about an execution method," Justice Kagan wrote.

Smith was represented by Robert M. Grass, Jeffrey H. Horowitz, David Kerschner, Ashley Burkett, Angelique A. Ciliberti and Lindsey Staubach of Arnold & Porter Kaye Scholer LLP and Andrew B. Johnson of Bradley Arant Boult Cummings LLP.

Alabama is represented by Edmund G. Lacour Jr., Robert M. Overing, Dylan Mauldin and Richard D. Anderson of the Alabama Attorney General's Office.

The cases are Smith v. Alabama, case numbers 23A688 and 23-6562, in the Supreme Court of the United States.

--Editing by Peter Rozovsky.