THE VEHICLE WAS PARKED ON AN INCLINE, FACING UP, AND PUT IN PARK. THE DRIVER EXITED THE VEHICLE AND THEN REACHED BACK IN TO TURN OFF AND REMOVE THE KEYS. THE VEHICLE STARTED TO ROLL BACK DOWN THE DRIVE, HITTING TWO OTHER VEHICLES BEFORE THE DRIVER, WHO WAS HIT BY THE OPEN DOOR, COULD GET BACK IN THE VEHICLE AND APPLY THE BRAKES. IT IS UNKNOWN WHY THE KEYS WOULD HAVE COME OUT IF THE CAR WAS NOT IN PARK, OR WHY THE CAR WOULD SWITCH FROM PARK TO REVERSE WITHOUT THE KEYS IN OR A FOOT ON THE BRAKE. *TR