A fire on the Southbury Training School campus is under investigation.  State Police say a bus stop gazebo was destroyed last week.  Emergency responders found the structure fully engulfed in flames Friday evening.  Witnesses reported a young female occupant exiting a white SUV stopped in front of the gazebo, running to the structure and setting off fireworks.  Troopers say the SUV was last seen going down Constitution Hill towards Main Street South.  Anyone with information is urged to call Connecticut State Police Troop A.