Believing his cellmate was the devil, John Setchel grabbed 72-year-old Ronald Sailers off of the top bunk in the Hall County Jail and slammed his head into the ground until he died, prosecutors said Friday morning.

Setchel, 24, of Dawsonville, pleaded guilty but mentally ill Friday to malice murder for Sailers' death on Oct. 5. A judge gave him a life sentence at the plea hearing at the Hall County Courthouse.

"He did refer to the victim as ‘devil' or ‘the devil,' and he had some belief that the devil would hurt him at some point," said Assistant District Attorney Kelley Robertson. "Alternatively, he also said he wasn't afraid of the devil and that he was angry at the roommate for using too much toilet paper - things of that nature."

According to evidence presented by Robertson, Setchel allegedly stomped Sailers while he was in a face-down position.

In an interview with Georgia Bureau of Investigation agents, Setchel referred to Sailers as the devil and claimed to be acting in self-defense, Robertson said.

Setchel underwent multiple mental evaluations and was later determined to be ultimately competent to stand trial and criminally responsible, Robertson said.

Robertson and the district attorney's office argued for life without the chance of parole.

Superior Court Judge Kathlene Gosselin said if she were to believe that Setchel could not become a more mature person later in life, she "would have to give up (her) faith in people completely."

"I'm not willing to believe that he will never mature beyond the age of 24," she said.

This story will be updated.