Such adjustments have happened before. When hangings were considered slow and grisly, and an unseemly form of public entertainment, executioners tried to improve things by using gallows instead of tree limbs, and then scaffolds instead of gallows, Ms. Denno has written. But the efforts were “plagued by guesswork and inconsistency,” she said.
Eventually, a New York State commission charged with making executions more humane came up with the electric chair. Its first victim, in 1890, twitched for half a minute after being pronounced dead, Ms. Denno wrote.
The U.S. Supreme Court has never invalidated an execution method. In 2018, it set a standard that the chosen method cannot “superadd” terror, pain or disgrace, said Robin Maher, the executive director of the Death Penalty Information Center. But prisoners who object to the proposed execution method must provide a feasible and readily available alternative, the court said.
In that 2018 case, the prisoner, Russell Bucklew of Missouri, had already suggested nitrogen hypoxia as an alternative but had been rejected. He was not the only prisoner to try to choose nitrogen gas. In 2022, Richard Atwood, a death-row prisoner in Arizona, requested that the state use nitrogen in the gas chamber instead of cyanide. Cyanide executions had been described as prolonged and agonizing. And Mr. Atwood’s mother was Jewish and had fled the Nazis, who used a form of cyanide in their gas chambers.
The state refused the request, and Mr. Atwood died of lethal injection.
Proponents of nitrogen hypoxia have called it a painless and “nearly perfect” method of execution. But experts, including Dr. Philip Nitschke, a pioneer in assisted suicide who has witnessed dozens of nitrogen hypoxia deaths, warned of a risk of substantial suffering should things go wrong. Death penalty opponents argue that the method is experimental and could prove dangerous to those administering it. Nitrogen gas has caused deaths in industrial accidents and has been used in physician-assisted suicides but had never been tested in a death chamber before Thursday evening.
Even if the execution of Mr. Smith appeared to proceed without unintended consequences, death penalty opponents said that suffering could be hard to observe. Autopsies of people killed by lethal injection have suggested that their pain was masked, rather than reduced, by paralytics.