Paul Belding pleaded guilty to 2nd degree felony murder. He was charged after an incident at the U.S. Oil convenience store at 22nd and Messanie June 13.
Police said Richard Gray, 77, tried to stop Belding from taking his van and in the process suffered a traumatic head injury.
Gray died June 18.
Buchanan County Circuit Judge Patrick Robb scheduled sentencing for November 18.