The Cook County Medical Examiner’s Office confirmed that the off-duty Chicago police officer fatally shot on Saturday morning is 23-year-old John Rivera.

The Chicago Police Department said that Rivera and three other individuals were sitting in a parked car when two men approached their vehicle and at least one of the offenders opened fire.

According to CBS News, another individual in the car was also struck. A second off-duty officer was also in the car and was not injured. The offenders fled on foot and remain at large.

Chicago Police Spokesman Anthony Guglielmi said on Twitter that investigators have been "working around the clock to follow evidence and review dozens of camera feeds. We continue to identify persons of interest based on the investigation and we are speaking to those individuals."