Demetrius Terrence Frazier has been executed using controversial nitrogen gas tonight for the rape and murder of Pauline Brown - he is just the fourth criminal to be executed using the method

Demetrius Terrence Frazier, 52, was executed using controversial nitrogen gas in the early hours of Friday morning - his mother begged for his life to be spared

An Alabama death row inmate who raped and murdered a woman in 1991 was executed this week using nitrogen gas, making him the fourth person in the U.S. to die by the controversial method.