POUND, Va. - For seven days, Robert Gleason Jr. begged correctional officers and counselors at Wallens Ridge State Prison to move his new cellmate. The constant singing, screaming and obnoxious behavior were too much, and Gleason knew he was ready to snap.

On the eighth day - May 8, 2009 - correctional officers found 63-year-old Harvey Gray Watson Jr. bound, gagged, beaten and strangled. His death went unnoticed for 15 hours because correctional officers had falsified inmate counts at the high-security prison in southwestern Virginia.

Now, Gleason says he'll kill again if he isn't put to death for killing Watson, who had a history of mental illness. And he says his next victim won't be an inmate.

"I murdered that man cold-bloodedly. I planned it, and I'm gonna do it again," the 40-year-old Gleason told The Associated Press. "Someone needs to stop it. The only way to stop me is put me on death row."

Gleason already is serving a life sentence for killing another man. He fired his lawyers last month - they were trying to work out a deal to keep him from getting the death penalty - so he could plead guilty to capital murder. He has vowed not to appeal his sentence if the judge sentences him to death Aug. 31.

"I did this. I deserve it," he said. "That man, he didn't deserve to die."

Watson was serving a 100-year sentence for killing a man and wounding two others in 1983 when he shot into his neighbor's house in Lynchburg with a 10-gauge shotgun. According to prison records, Watson suffered from "mild" mental impairment and was frequently cited for his disruptive and combative behavior.

Watson was sent to Wallens Ridge on April 23, 2009, a day after he set fire to his cell at Sussex II State Prison. Gleason and Watson became cellmates on May 1, 2009.

In the days the two spent locked in an 8-by-10-foot cell, Watson would talk about how he had "drowned" two television sets because they "had voodoo in them," Gleason said.

He would also belt out "I wish I was in the land of cotton" from the song "Dixie" and other songs at all hours, scream profanities and masturbate. In the chow hall and in the recreation yard, Watson would get inmates to give him cigarettes for drinking his urine and clabbered milk.

"You can't be upset with someone like that," Gleason said. "He needed help."

Gleason said his requests to separate the two were met with mockery and indifference by correctional officers and prison counselors. He said he knew what he would do once officials refused to put Watson in protective custody.

"That day I knew I was going to kill him," he said. "Wallens Ridge forced my hand."

It was after midnight when Gleason used slivers of bed sheets to tie Watson's hands and arms to his body and fashioned a gag out of two socks. He later removed the gag and gave Watson a cigarette, telling him it would be his last. Gleason said Watson spit in his face when he went to take the cigarette out of Watson's mouth, so he jumped on his cellmate's back and beat and strangled the man.

He then covered Watson's body with a bed sheet to make it look like he was sleeping.

Gleason kept Watson's death a secret through two mandatory standing counts and two meals. Officers only discovered the body when Watson's psychiatrist came to see him at 4:40 p.m. and found him dead, according to court documents.

Prison employees involved in the case denied repeated requests for comment from the AP. Department of Corrections spokesman Larry Traylor also declined to discuss the situation, but said that two officers were disciplined and two others were fired. One of the fired officers was reinstated upon appeal.

Gleason has since been transferred to the "supermax" Red Onion State Prison.

Watson's sister, Barbara McLeod of Longmont, Colo., said Gleason should be forced to spend the rest of his life in prison with no privileges.

"He doesn't deserve to be able to control his own destiny at this point. He doesn't deserve to have his death on the conscience of the state of Virginia," she said.

McLeod said her brother had a history of mental problems that grew worse during his last decade of incarceration. McLeod said she's upset that her brother was housed with such a violent prisoner - and angry that it took so long for guards to realize he was dead.

"Supposedly they are monitoring these prisoners," she said. "I guess not."

During a hearing a week before his June 1 trial was to start, Gleason warned Wise County Commonwealth's Attorney Ron Elkins that he would kill again if Elkins didn't seek the death penalty.

Elkins had offered to let Gleason plead to second-degree murder.

He also offered to drop the capital murder charges and come back with a charge that didn't carry a death sentence. Elkins wouldn't say why he made those offers.

However, capital murder cases are typically lengthy and expensive, especially as appeals wind through the courts. Even though Gleason confessed, Elkins said he proceeded cautiously to ensure the case couldn't be overturned on appeal.

Court records show that Gleason told Elkins he had no remorse for killing Watson. He said he learned from his father to own up to his mistakes, and that he needed to prove to his loved ones that actions have consequences.

"There's nothing you guys can do to me to hurt me. Nothing," he told the prosecutor. "But there's something you guys can do to prevent someone else from getting hurt."