HOWEVER, for those quick to criticise the victim, the Kingair has been known for the poor door locking & warning mechanism, such that when one shuts the door, if one checked the position of the locking barrels against the lugs, one can ignore a subsequent door warning.
Kingair doors have also been known to open in flight. One famous incident, circa 1980's (I think), saw a Kingair Captain investigate a door warning in flight, leaving the Co-pilot at the controls. The door opened, the Captain went out, and was found once landed, hanging upside down with a death-grip on the lower door supports.
From this thread, it's not possible to say for sure, if the victim opened the door, or, perhaps, it opened on him, and he wasn't as lucky as the aforementioned Captain.
Well, good post, but...
The WARNING itself is from a microswitch with a arm and a little roll, when poorly adjusted (mainly when adjusted in warm climate) it gives spurios or continuos warning (RED LIGHT on Warn panel). Problem is the shrinking of metal in the cold. The early issues with I think a total of 5 lost doors is solved since roughly 25 years ago, and to my knowledge there has been no lost doors ever since. The dor is attached on the bottom with piano type hinge and one cable (second is an option)plus the damper. There have been incidences when the damper didnt work, the door hinge became partly ruptured, but has nothing to do with this incident. I would think that the damper is the strongest attachment to the airframe. BTW there are also 2 hooks on the top of the door (opposite side of the hinge) that pull the door in, connected to the rotate handle as the plungers are.
The check after closing the door is to look at all 4 plungers (green tape at mark) then lift one door step and check a red plate that goes around a round piece. That thing is lighted, versus the unlighted 4 plunger holes.
Nothing is impossible, but a malfunctioning door mechanism or improper closed door is what I consider less likely.