Alan Eugene Miller was executed Thursday evening in Alabama, state officials said, making him the second inmate known to die by nitrogen hypoxia, a controversial method critics say is tantamount to torture.

Alan Eugene Miller, 59, was pronounced dead last Thursday at 6:38 p.m. local time at this south Alabama prison after nitrogen gas was used to execute him, convicted of “killing three people in back-to-back workplace shootings,

Alan Eugene Miller, 59, is scheduled to be executed with nitrogen gas at a south Alabama prison. Miller was convicted of killing three men — Lee Holdbrooks, Christopher Scott Yancy and Terry Jarvis — in back-to-back workplace shootings in 1999.

Alabama executed a convicted murderer Thursday evening for the deaths of three co-workers during separate workplace shootings more than two decades ago.

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.

Lawyers for death row inmate Carey Dale Grayson are attempting to block his coming execution by nitrogen hypoxia.