MONTGOMERY, Ala. — Alabama has scheduled a September execution by nitrogen gas for a man convicted of killing a convenience store clerk during a 1997 robbery.

Alabama Gov. Kay Ivey set a Sept. 25 execution date for Geoffrey Todd West. West, now 49, is on the death row for killing Margaret Parrish Berry.

Prosecutors said West drove to Harold’s Chevron in Attalla with plans to rob the store where he once worked. Berry, 33, was shot in the back of the head while lying on the floor behind the counter, prosecutors said.

Court records state that $250 was taken from a cookie can that held the store’s money.

A jury convicted West of capital murder and voted 10-2 to recommend a death sentence. A judge adopted the jury’s recommendation and sentenced West to death.

Etowah County Circuit Judge William Cardwell during the 1999 sentencing said it was difficult to order the execution of a young man but said the shooting death was “clearly deliberate and intentional, carried out execution style.”

Prosecutors also charged West’s girlfriend with the slaying. She pleaded guilty and was sentenced to 35 years in prison.

Alabama last year became the first state to carry out an execution with nitrogen gas, a method that involves pumping nitrogen through a face mask and depriving the inmate of oxygen.

The method has now been used in six executions — five in Alabama and one in Louisiana. Alabama has scheduled another nitrogen execution in August.

West was one of several Alabama inmates who selected nitrogen as their preferred execution method after state lawmakers authorized the method. He made the selection before Alabama developed procedures for the method.