VEHICLE WAS IN PARK POSITION ON A SIDE ROAD. IT WAS STILL RUNNING SINCE WE WEREN'T GOING TO REMAIN PARKED THERE EXCEPT FOR A FEW MINUTES. I WAS TAKING PICTURES OF MY SON BEFORE HIS BAND CONCERT NEAR THE SCHOOL WHERE THE VEHICLE WAS PARKED. IT REMAINED STATIONARY/PARKED FOR UP TO 4 MINUTES AT WHICH POINT IN TIME IT STARTED ROLLING DOWN THE INCLINED ROAD UNATTENDED. HAVE NO IDEA WHAT PART OF THE CARE MALFUNCTIONED TO SWITCH IT OUT OF PARK. SO UNKOWN.