Brad Sigmon, who admitted to killing his ex-girlfriend's parents, said he chose to die by bullets because he considered the other choices offered by the state to be worse.

The last time such an execution took place was 15 years ago, in Utah. The South Carolina inmate chose the method because of his concerns about lethal injection, his lawyer said.

A convicted double murderer has been executed by firing squad, the first such execution in the United States since 2010, according to the South Carolina Department of Corrections.