The state has called its new protocol "the most painless and humane method of execution known to man."
United Nations human rights experts and lawyers for Smith, who survived Alabama's previous botched attempt to execute him by lethal injection, had sought to prevent it, saying the method was risky and could lead to a torturous death or non-fatal injury.
Alabama prison officials and journalists who observed Smith's execution were due to brief reporters shortly.
(Reporting by Jonathan Allen; Editing by Lincoln Feast.)
