VEHICLE RUNNING IN PARK WHILE DRIVER GATHERED BOXES TO PLACE IN BED OF TRUCK. DRIVE TRAIN ENGAGED SENDING DRIVERLESS VEHICLE DOWN ROAD, ACROSS INTERSECTION AND INTO BRICK WALL. WITNESS TO IMPACT RAN TO VEHICLE THINKING TO CHECK ON DRIVER. UPON OPENING DOOR, NOTED NO DRIVER AND STATED SHIFTER STILL INDICATED VEHICLE WAS IN PARK.