A South Carolina man who killed his ex-girlfriend's parents with a baseball bat was executed by firing squad Friday, the first U.S. prisoner in 15 years to die by that method, which he saw as preferable to the electric chair or lethal injection.

Three volunteer prison employees used rifles to carry out the execution of Brad Sigmon, 67, who was pronounced dead at 6:08 p.m.

Sigmon killed David and Gladys Larke in their Greenville County home in 2001 in a botched plot to kidnap their daughter. He told police he planned to take her for a romantic weekend, then kill her and himself.

Sigmon's lawyers said he chose the firing squad because the electric chair would "cook him alive," and he feared that a lethal injection of pentobarbital into his veins would send a rush of fluid and blood into his lungs and drown him.

The details of South Carolina's lethal injection method are kept secret in the state, and Sigmon unsuccessfully asked the state Supreme Court on Thursday to pause his execution because of that.

On Friday, Sigmon wore a black jumpsuit with a hood over his head and a white target with a red bullseye over his chest.

The armed prison employees stood 15 feet (4.6 meters) from where he sat in the state's death chamber — the same distance as the backboard is from the free-throw line on a basketball court.

The volunteers all fired at the same time through openings in a wall. They were not visible to about a dozen witnesses in a room separated from the chamber by bullet-resistant glass.

Witnesses included three family members of the Larkes. Also present were Sigmon's attorney and spiritual adviser, a representative from the prosecuting solicitor's office, a sheriff's investigator and three members of the news media.

Sigmon's lawyer read a closing statement that he said was "one of love and a calling to my fellow Christians to help us end the death penalty."

The firing squad is an execution method with a long and violent history in the U.S. and around the world. Death in a hail of bullets has been used to punish mutinies and desertion in armies, as frontier justice in America's Old West and as a tool of terror and political repression in the former Soviet Union and Nazi Germany.

Since 1977 only three other prisoners in the U.S. have been executed by firing squad. All were in Utah.

In South Carolina on Friday, a group of protesters holding signs with messages such as "All life is precious" and "Execute justice, not people" gathered outside the prison before Sigmon's execution.

Supporters and lawyers for Sigmon asked Republican Governor Henry McMaster to commute his sentence to life in prison. They said he was a model prisoner trusted by guards and worked every day to atone for the killings and also that he committed the killings after succumbing to severe mental illness.

But McMaster denied the clemency plea. No governor has ever commuted a death sentence in the state, where 46 other prisoners have been executed since the death penalty resumed in the U.S. in 1976. Seven have died in the electric chair and 39 others by lethal injection.