(WTTW News)

A detainee at the Cook County Jail died Monday after he was found unresponsive in his cell.

According to the Cook County Sheriff’s Office, 33-year-old Michael O’Connor was found unresponsive in his cell in the jail’s Residential Treatment Unit at around 4:30 p.m. Christmas day.

“Security staff and medical staff from Cermak Health Services immediately began life-saving measures and called 911,” the sheriff’s office said in a statement. “The Chicago Fire Department transported O’Connor to Mt. Sinai Hospital, where he was later pronounced deceased.”

The Illinois State Police Public Integrity Task force is conducting an investigation into his death. According to the sheriff’s office, foul play is not currently suspected in O’Connor’s death. The Cook County Medical Examiner’s Office will determine the official cause and manner of death.

O’Connor had been held in the jail since July, when he was issued a $100,000 D-bond on felony charges of aggravated intimidation of a peace officer, intimidation/physical harm, threatening a public official and harassment/obscene proposal/threat to kill. The sheriff’s office said he had allegedly sent multiple threatening and obscene messages to a Chicago police officer.

Cook County and the rest of Illinois ended the use of cash bail in September.

While in custody, O’Connor was subsequently charged with two additional counts of felony aggravated battery to correctional staff.