THE AIRPLANE LANDED NORMALLY. THE PILOT FELT A VIBRATION AND THE AIRPLANE PULLED LEFT DURING ROLLOUT. HE HEARD A LOUD SNAPPING SOUND AND THE LEFT SIDE OF THE AIRPLANE DROPPED TO THE RUNWAY. THE AIRPLANE PULLED SEVERELY LEFT AND DEPARTED THE RUNWAY AND STOPPED IN THE GRASS ABOUT 30 FEET FROM THE RUNWAY. EXAMINATION OF THE LANDING GEAR REVEALED A NUT, WASHER, AND COTTER PIN WERE MISSING FROM THE LEFT GEAR TORQUE-LINK ATTACHMENT TWO HOURS HOBBS TIME AFTER THE ACCIDENT OCCURRED. WORK HAD BEEN PERFORMED ON THE LEFT GEAR TORQUE LINK ATTACHMENT DURING THE LAST INSPECTION.