TULSA, Oklahoma - The mother of an Oklahoma prisoner wants to know why her son died after being beaten behind bars.

Department of Corrections officials say guards found John Vaughan in his cell at the Conner Correctional Facility in Hominy before taking him to the hospital.

Vaughan's mother, Brenda Vaughan, believes prisoners beat him to death. She said she pleaded with prison officials to get her son transferred out of the Dick Conner Correctional Facility in Hominy.

"I got the feeling from my son he was scared to death to talk to anybody because he was afraid that would be his last day,” she said. “My son thought he was going to die all month."

He'd only been at the medium security prison for a couple months, on theft and assault convictions, when Brenda said her son started to get harassed about owing money to other prisoners.

She said she sent thousands of dollars to her son to keep him out of trouble.

She even received a text message from her son saying, "Mom, I'm not lying, I can't take no more of this."

Brenda said it was almost like the other prisoners were holding her son hostage.

"I just don't understand why these gentlemen felt like they had to kill my son," she said.

Brenda learned her son died Thursday after guards found him in his cell after a fight. DOC officials say guards took Vaughan to the medical ward and eventually to the hospital where he died.

"He didn't have a chance. And when you're put away for so many years you go through a lot as a parent, because, whatever happens through your family you feel it. Regardless of why he was there, he didn't deserve to die for owing someone money," she said.

Vaughan's body is with the medical examiner's office and will determine the cause of death; but his mother believes she knows what happened saying, “They beat him to death. They beat him to death.”

DOC officials say corrections detectives are reviewing security cameras and interviewing prisoners.