A prisoner in Alabama has become the first inmate in the world to be executed with nitrogen gas.
Convicted murderer Kenneth Smith was put to death on Thursday after the US Supreme Court declined his legal bid to halt his execution.
The use of nitrogen gas as a method of execution is highly controversial and had never been used before in the US.
It involves clamping a mask tightly to the face, covering the mouth and nose. The mask is then fed with nitrogen gas. The person continues to breathe normally, but with no oxygen present the body gradually shuts down until death occurs – effectively they are suffocated.
Smith’s execution comes after he survived a botched lethal injection in 2022 which helped prompt a review of the state’s death penalty procedures.
A humane death or a lethal experiment? How Alabama’s controversial nitrogen execution works
The Supreme Court justices declined to uphold Smith’s legal challenge that claimed a second execution attempt by Alabama – after the first failure caused him severe trauma – would violate the US Constitution’s 8th Amendment protections against cruel and unusual punishment.
However the decision was not unanimous, with three justices voting to halt the execution.
“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,” Justice Sonia Sotomayor wrote, saying she would have granted the injunction.
“The world is watching.”
Just minutes before the execution was carried out, the Supreme Court refused for a second time to intervene to stop it going ahead.
Smith was also separately contesting the legality of Alabama’s nitrogen gas protocol, which his lawyers previously called “a novel method of execution that has never been attempted by any state or the federal government”.
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