ACCORDING TO THE AIRPORT MANAGER, THE PILOT HAD JUST COMPLETED A FLYBY OF THE RUNWAY AND WAS IN THE PATTERN TO LAND. THE WITNESS NOTICED THAT ON FINAL APPROACH, THE PILOT HAD NOT LOWERED THE LANDING GEAR. THE PILOT STATED THAT HE HAD NOT PERFORMED A COMPLETE, BEFORE-LANDING CHECKLIST AND HAD FORGOTTEN TO LOWER THE GEAR. AFTER THE PROPELLER BLADE TIPS STRUCK THE RUNWAY, THE PILOT ADDED POWER TO GO AROUND BUT THEN DECIDED TO MAKE A GEAR-UP LANDING. THE AIRCRAFT OVERRAN THE RUNWAY AND COLLIDED WITH TERRAIN.