Jefferson City Correctional Center inmate Danny Kittrell, 68, was pronounced dead at 5:35 a.m. Wednesday morning.
Kittrell was serving a life sentence for first-degree murder, capital murder, two counts of armed criminal action, forcible rape and robbery from St. Louis.
Kittrell began serving his sentence on Sept. 11, 1987.
The Missouri Department of Corrections said an autopsy will be conducted.