CHESTER, Ill. -- The death of a Menard Correctional Center inmate who succumbed to hypothermia in an unheated cell was an accident, a coroner's jury has ruled.

Charles Platcher's death on Christmas Day was an accident because the heat in the building had malfunctioned, the six-member Randolph County coroner's jury declared Tuesday.

Platcher, 31, of McHenry County was serving a 40-year sentence for killing his mother when he was placed on "strip-cell suicide watch" at the prison Dec. 15, Corrections Department investigator Richard Harrington told the jury.

He was placed in a solitary cell in the prison's health-care unit without clothing and with a single blanket, Harrington said.

Prison records show guards checked Platcher every 10 minutes by looking through a window into his cell.

It was 60 degrees in the cell a few hours after his death, when it was 26 degrees outside the prison, Harrington told the jury.

Three prison employees were disciplined after the incident.

Randolph County State's Attorney Darrell Williamson said Tuesday he hadn't decided whether to bring criminal charges in the case. Williamson did not immediately return a telephone message left Wednesday by The Associated Press.