In a White House press conference on Friday afternoon, White House spokesperson Karine Jean-Pierre said the administration of President Joe Biden is concerned about Alabama’s method of execution.

“The reports of Kenneth Smith and his death last night, obviously, is troubling,” Jean-Pierre said. “The use of nitrogen gas, it is troubling, of course.”

The first-ever execution by nitrogen hypoxia “underscores why the president supports the attorney general’s moratorium on federal death penalty, pending review of the policies and procedures governing its use,” she said.

“The president has long said and has had deep, deep, deep concerns with how the death penalty is implemented and whether it is consistent with our values,” Jean-Pierre said.

Alabama Attorney General Steve Marshall said Thursday night’s execution went according to plan for the never-used method.

Smith was executed for the 1988 murder of Elizabeth Dorlene Sennett in Colbert County.

Witnesses said Smith writhed and showed convulsive movements for about two minutes after the nitrogen gas was started.

“When they turned the nitrogen on, he began to convulse, he popped up on the gurney over and over and over and over again. He shook the whole gurney,” Smith’s spiritual adviser, the Rev. Jeff Hood, said after witnessing the execution.

“I could hear audible gasps coming behind me from the witness area. I could see the corrections officers that were in there….I think they were very surprised that it didn’t go smoother.”

The U.S. Supreme Court declined to halt the execution to review claims that it violates the constitutional ban on cruel and unusual punishment and deserved more legal scrutiny before it was used on a person.

Justice Sonia Sotomayor, who along with two other liberal justices dissented, wrote, “Having failed to kill Smith on its first attempt, Alabama has selected him as its ‘guinea pig’ to test a method of execution never attempted before. The world is watching.”

In her dissent, Sotomayor said Alabama has shrouded its execution protocol in secrecy, releasing only a heavily redacted version. She added that Smith should have been allowed to obtain evidence about the protocol and to proceed with his legal challenge.

“That information is important not only to Smith, who has an extra reason to fear the gurney, but to anyone the State seeks to execute after him using this novel method,” Sotomayor wrote.

“Twice now this Court has ignored Smith’s warning that Alabama will subject him to an unconstitutional risk of pain,” Sotomayor wrote. “I sincerely hope that he is not proven correct a second time.”

The Associated Press contributed to this report.