Miller was convicted of murdering three co-workers during two back-to-back shootings one morning in 1999 in suburban Birmingham.

Alabama used nitrogen gas Thursday to execute a man convicted of killing three people in back-to-back workplace shootings, the second time the method that has generated debate about its humaneness has been used in the country Alan Eugene Miller,

Alabama executed a death row inmate Thursday with nitrogen gas, a controversial and highly secretive procedure that has only been done one other time.