Carey Dale Grayson scheduled to be killed for 1994 murder by technique that previously caused visible signs of distress

Alabama is hours away from carrying out its third execution this year using the controversial new method of nitrogen gas, a technique that in previous state killings caused visible signs of distress.

Barring a last-minute appeal to the US supreme court, Carey Dale Grayson will be put to death on Tuesday evening for the 1994 murder of a hitchhiker. The prisoner will have a mask strapped to his face through which nitrogen will be pumped, causing fatal oxygen deprivation.