One other state, Oklahoma, allows for death by firing squad but only if the lethal injection process is ruled unconstitutional by a court.

Why the firing squad?

Since 2011, the Europe-based manufacturers of the most common execution drugs have refused to sell them to American prisons. They flat-out disagree with the practice, and hope that cutting off the source of the drugs will eventually lead the US to stop executing people.

The Guardian's Ed Pilkington reported on the boycott at the time: "Though the new restricted list covers the only two drugs currently used in American death penalties, the fear is that intrepid states will find a way round the controls by using other sedatives not on the list."