During the initial climb after takeoff, one of the crew members reported that the right engine lost power and that they would return for a landing. The aircraft was observed to circle to the left with the right propeller feathered. During the turn to the airport, the aircraft descended and crashed in a swampy area that was surrounded by trees. A post-impact fire erupted and destroyed the aircraft. Subsequent investigation verified that the right engine propeller had been feathered. The fuel selector for the right engine was found positioned between 'off' and 'on.' The magneto switch for the left engine was found in the 'off' position, while the magneto switch for the right engine was in the 'both' position. Remnants of the throw-over yoke showed that it was positioned to the copilot's side. The copilot's flight time in the Beech 58 was not verified. Both engines were removed and prepared for operational checks. After water contamination was cleaned from the engines, both were started and ran successfully.