Surveillance footage, which has just been released, showed the off-duty Chicago police officer sitting in a black BMW on April 20

Two men approached, and the first climbed in the passenger seat and appeared to pull an object out of his pocked

The off-duty cop quickly climbed out the driver's seat, as the carjacker's accomplice got in

The officer began shooting at the thieves, who returned fire before fleeing

No-one was hurt in the shootout, and no arrests have been made

Witness Keith Harris said: 'They ran into the wrong guy at the wrong time'