At 1317 Eastern time, the aircrafts right main landing gear collapsed during the landing roll; the airplane came to rest in the mud on the right side of the runway. The Commercial pilot and copilot were uninjured; the airplane sustained substantial damage. According to the flight crew, after takeoff they could not get the right gear to fully retract. The crew declared an emergency and proceeded to land. Examination of the right main landing gear found the upper portion of the gear trunnion fractured and pulled out of the forward wing spar. Damage to the wing consisted of the forward spar, and the flap.