A comment and a reply to that comment I saw...
Comment 1:
"Probably best in the future to idle both engines and descend to maintain speed while everyone is out on the door. I understand why the pilot idled #1, for the jumpers, but asymmetrical thrust while at high altitude, low speed, atypical drag situation, disrupted airflow to the tail, and bad CG, is a perfect recipe for a spin."
Reply to that Comment:
"Me thinks this is a perfect Vmc demonstration. I think the mistake was the quick change in CG as the jumpers headed towards the door. Did you notice just right before this event happened the nose of the King Air pitched up.
Slow flight just above Vmc with an immediate change in Aft CG caused the venerable Stall / Spin and Recovery which btw was videoed nicely the jumper.
Just my two cents but I would like to see some NTSB or similar explanation"
I know nothing of the aircraft, so I don't know her quirks, especially when it comes to load shifting like that. If someone knows someone who's done a lot of skydiver transport with this aircraft, give em a ring. They should be able to give you a decent idea of what happened.
EDIT: I get the feeling Columbo would have had a good idea of how this played out.