A Stateville Correctional Center inmate died Sunday afternoon at a Chicago hospital of natural causes, an autopsy found.

Dewayne Keenan, 57, died at 2:50 p.m. Sunday at Mount Sinai Hospital, according to the Cook County medical examiner’s office and Illinois Department of Corrections spokeswoman Nicole Wilson.

Keenan was on medical furlough from the prison in southwest suburban Crest Hill, where he was serving a 14-year sentence for aggravated DUI and driving on a revoked or suspended license, according to IDOC records. He had been in prison since Dec. 4, 2014.

Keenan had previously served sentences for reckless driving, DUI, theft and burglary, according to IDOC records.

An autopsy Wednesday found he died of peritonitis, or inflammation of the abdomen wall, and liver disease was listed as a contributing factor, according to the medical examiner’s office. His death was ruled natural.