U.S. death penalty: Alabama to use nitrogen [Video]

Alabama is preparing to carry out the nation’s second nitrogen gas execution Thursday as disagreements continue over the humaneness of the new method of putting prisoners to death.

Alan Eugene Miller, 59, is scheduled to be executed with nitrogen gas at a south Alabama prison two years after the state previously attempted to execute him by lethal injection. Miller was convicted of killing three men — Lee Holdbrooks, Christopher Scott Yancy and Terry Jarvis — in back-to-back workplace shootings in 1999.

In January, Alabama put Kenneth Smith to death in the first nitrogen gas execution, a new method that involves placing a respirator gas mask over the inmate’s face to replace breathable air with pure nitrogen gas, causing death by lack of oxygen.

Alabama officials and advocates have argued over whether Smith suffered an unconstitutional level of pain during his execution after he shook in seizure-like spasms for more than …