Death row inmate Cary Grayson is the third person in the world to be executed by nitrogen inhalation on Thursday in Alabama, a controversial execution method that has sparked protests.

“Alabama successfully used the hypoxic method of execution by inhalation of nitrogen to execute Cary Grayson,” state Attorney General Steve Marshall said in a statement.

Grayson was sentenced to death in 1996 for the murder, thirty years ago, of a woman hitchhiking in Alabama. The victim, Vicki DeBlier, 37, hitchhiked from Tennessee to visit her mother at her home in Louisiana. Her body was found riddled with knives and posthumously mutilated.

According to reporters present at the execution, Cary Grayson cursed at the prison warden when the warden asked him if he had any last words to say. Then, as the gas began to flow into the mask over his face, he would shake his head from side to side.

The 49-year-old struggled to breathe for several minutes before he stopped moving, they found.

As with the previous two executions by nitrogen inhalation, in February and September — both in Alabama — UN experts warned against the use of the method last Wednesday, arguing that it could be a form of “torture” and that it was clearly ” prohibited by international law”.

Grayson’s execution is the 6th in Alabama and the 22nd in the US since the beginning of the year.

Except for the three by nitrogen inhalation, all others were carried out using lethal injection solutions.

The death penalty has been abolished in 23 of the 50 US states. Another six (Arizona, California, Ohio, Oregon, Pennsylvania, and Tennessee) have moratoriums on executions by governor.