HAZEL CREST, IL — A Chicago Police Department officer shot and killed someone who was attempting to rob him during a sales transaction that initiated online Tuesday night in Hazel Crest, police in the south suburb said. Police arrived on Birchwood Drive to a report of an armed robbery and related shooting at 9:54 p.m., when they met a man in plain clothes who identified himself as a Chicago police officer. A preliminary investigation indicates the officer shot and killed one of the two offenders while the other one remains at large as of late Wednesday afternoon.

Hazel Crest police will continue to investigate the armed robbery aspect of the incident while Illinois State Police will begin a use of force investigation into the shooting, which involved the police officer acting while off-duty. Police said in a news release Wednesday that when they arrived at the scene, the Chicago police officer had his arms in the air, identified himself as a police officer and notified police on the scene that he had a weapon and of its location. The deceased individual was found between two houses on the block with a police badge next to his body.

The off-duty cop was at the location to buy a computer from the two alleged offenders as a result of a sales transaction that initiated in an online sales network, according to the initial investigation. But when they met in person in Hazel Crest, one offender pulled out a handgun and ordered the off-duty officer to empty his pockets. It was then when the offenders found the off-duty officer's badge and weapon. Police said they took the badge, but before they were able to disarm him the off-duty officer fired at both of them, striking and killing one.