Authorities are investigating after an Arkansas prison inmate was found dead Monday, the state Department of Correction reported.

Charles Winston, 60, was found unresponsive in his cell about 9:30 p.m. at the Maximum Security Unit in Tucker, according to the state prison system. Medical personnel pronounced him dead at 9:55 p.m.

Arkansas State Police and the Department of Correction are investigating.

Winston had been serving a life sentence as a habitual offender after being convicted of kidnapping, aggravated robbery and first-degree battery in 2006.

Ten Arkansas prison inmates have reportedly died since Aug. 9. Two were suicides. The rest died under circumstances similar to Winston’s. They were found unresponsive or in medical distress and later pronounced dead.

Winston is the third inmate to died at the Maximum Security Unit in that time.