A judge in Alabama has issued a stay for a convicted killer’s upcoming execution while state officials investigate whether he is competent enough to be put to death.

David Lee Roberts, 59, was scheduled to be executed on Aug. 21 for the 1992 shooting death of Annetra Jones, but Marion County Circuit Judge Talmage Lee Carter temporarily stayed the execution until it can be determined if Roberts has a “rational understanding” of what would happen to him.

“Or similarly put, the issue is whether the petitioner’s concept of reality is so impaired that he cannot grasp the execution’s meaning and the purpose or the link between his crime and its punishment,” he wrote in the ruling.

Carter said the execution will remain on hold until the Alabama Department of Mental Health concludes its report on Roberts.

Roberts was set to die by nitrogen gas, a controversial method Alabama began using last year. (AP)

Roberts murdered Jones in Marion County on April 22, 1992, while he was staying at a house her boyfriend lived in. 

Prosecutors said Roberts arrived at the home, packed his belongings, stole money and shot Jones three times in the head with a .22 caliber rifle while she was sleeping on the couch. He then poured flammable liquid on her body and the floor and set the house on fire.

Jurors convicted him of capital murder and voted 7-5 that he receive life in prison without parole. However, a judge overrode that recommendation and sentenced him to death. 

Alabama no longer allows judges to override jury sentences in capital cases.

The Associated Press contributed to this report.