DENISON, TX - Denison police arrested a man for murder in the death of a Denison teenager.

Denison police say Robert Gray, 51, murdered 15-year-old Brandon Leon White. According to a court affidavit, Gray was the boyfriend of White's mother.

Authorities say White died of asphyxiation, after he was bound and gagged.

An affidavit shows White was diagnosed with autism and bi-polar disorder.

Grayson County District Attorney Joe Brown said the family used violence to deal with the teen's issues, like tying his wrists and ankles when he had medical-related fits.

"There's lots of evidence that he was bound, he had a history of behavior because of his medical condition that the parents couldn't control," Brown said. "And that's the way they chose to deal with it. And it was tragic."

Police believe Gray hit White in the face sometime Monday night or Tuesday morning. According to the affidavit, Gray called EMS around 2 a.m. Tuesday, almost two hours after he realized the boy was dead.

"Really a tragic situation. A kid that had had a really tough time, had medical situations, had a terrible family life it looked like," Brown said. "And this was as bad as they get as far as how children are treated."

Officials are charging Gray with murder - which, if convicted, is punishable by up to 99 years in prison.

Denison Police Lt. Mike Eppler said they're still investigation the case, and could file additional charges.

"If they haven't been talked to or contacted by an officer, please get a hold of us and let us know, because we would like to talk to them," he said. "Even if you think that what you have may be very insignificant, it could be something very important to the investigation."

Gray has a history of run-ins with the law.

He's a convicted felon. His past charges include robbery with a knife, burglary, possession of narcotics and rape.

He remains in Grayson County jail on a $500,000 bond.