VEHICLE HAD BEEN DRIVEN APPROXIMATELY 2 MILES FROM START TIME, WAS STATIONARY AND UNOCCUPIED FOR APPROXIMATELY 10-25 MINUTES. VEHICLE INTERIOR CAUGHT FIRE AT THE BASE OF THE TOP SITTING AREA OF THE REAR SEAT, FLAMES FROM FIRE MELTED THE OVER HEAD INTERIOR LIGHT AND IGNITED A FIRE ON THE HEAD LINER, WHICH CAUSED THE FIRE TO SPREAD UNDER NEATH THE HEADLINER AND ROOF OF THE VEHICLE, MELTING THE EXTERIOR PAINT. THERE WAS NO PRIOR INDICATION OF BURNING WHEN DRIVING OR AFTER PARKING THE VEHICLE PRIOR TO THE FIRE. FIRE DEPARTMENT ADVISED IT WAS BELIEVED TO BE RELATED TO REAR SEAT HEATERS MALFUNCTIONING CAUSING COMBUSTION THAT LEAD TO AN INTERIOR FIRE. DOORS WERE LOCKED PRIOR TO THE FIRE, AND STORE SURVEILLANCE DIDN'T SHOW ANY SIGNS OF EXTERIOR TAMPERING WITH THE VEHICLE.