COLDWATER TOWNSHIP, Mich. (WOOD) — Convicted serial killer Danny Ranes died while in prison last week.

Lakeland Correctional staff found Ranes unresponsive on Jan. 29, a spokesman with the Michigan Department of Correction said. Staff and first responders attempted lifesaving measures until he was pronounced dead by a doctor from an area hospital.

Michigan State Police are investigating his death, and the initial investigation shows no signs of foul play or drug use.

An autopsy is scheduled to be performed to determine the cause of death.

Ranes was serving multiple life sentences for raping and killing four women in the 1970s.