For as long as America has had the death penalty, there have been questions about how best to carry it out. The execution of Kenneth Eugene Smith in Alabama on Thursday, the first American execution in which death was caused by suffocation with nitrogen gas, gave no indication of settling the legal, moral and technical questions that have long bedeviled states as they mete out the ultimate punishment.

Most recently, problems with the purchasing, administration and effects of lethal injection drugs have sent states scrambling for alternatives ranging from the old — firing squads, electric chairs and gas chambers — to the untested, like Alabama’s use of a mask to force Mr. Smith to inhale nitrogen instead of air.

But after Mr. Smith’s death, the Alabama attorney general, Steve Marshall, hailed the execution as a “historic” breakthrough. He criticized opponents of the death penalty for pressuring “anyone assisting states in the process.”

“They don’t care that Alabama’s new method is humane and effective, because they know it is also easy to carry out,” he said in a statement.

Beginning in 2015, Oklahoma, Mississippi and then Alabama became the first three states to authorize the use of nitrogen hypoxia in executions. Oklahoma and Mississippi specified it as a backup method if lethal injections were ruled unconstitutional or if the drugs used in them became unavailable. Alabama offered death-row inmates a choice between nitrogen hypoxia and lethal injection.

Mr. Smith chose nitrogen after he survived an hourslong attempt to execute him by lethal injection in 2022, during which he was repeatedly stabbed with needles and placed in what he called an “inverted crucifixion position.” But he continued to wage a legal battle against the use of the method and the state’s protocol for administering it.