all indications being that the pilot voluntarily jumped after taking advantage of the brief moment when his colleague was watching the paratroopers
Very sad if this is indeed the case, but there are still several big questions . If the other pilot was in the cockpit monitoring the parachutists, how could he/she not notice the deceased pilot unstrapping and opening the door? If in the cabin, it is surprising that the deceased pilot managed to unstrap and climb out of a snug cockpit without disturbing the flying controls. And if it was a jumpmaster in the back rather than a co-pilot, then he/she did rather well to land the aircraft safely afterwards.