The Oklahoma Department of Corrections is investigating the death of an inmate at the Oklahoma State Penitentiary Sunday evening.
In a news release, the DOC says Mark Stacey, 43, was found unresponsive in his cell at about 7 p.m. Sunday.
He was pronounced dead at 7:21 p.m.
Officials at the Oklahoma State Penitentiary say Stacey had a cell mate, but early indications showed no apparent trauma or wounds on Stacey.
The cause of death will be determined by the Oklahoma Medical Examiner's Office.
Mark Stacey was serving time out of Oklahoma County for possession of a controlled and dangerous substance and possession of contraband in a penal institution.