Very sad for this young lad.
Maybe he was retrieving the door pin.
The Q400 MLG Aft doors are hydraulically operated. They can be opened for maintenance by pulling the free fall handle in the F/D roof, but this resets as soon as it is released. If AC power is on then the SPU (AC pump) and PTU are required to close the doors.
The door lock pin should be installed when anyone is working in the MLG bay. The problem is that to fit the pin you have to be inside the bay first and if someone turns on the pump before you fit the pin, the doors will close, or, if you remove the pin you are vulnerable until you are clear of the doors.
On the line, we normally only have DC power available so the danger does not arise as no hydraulics can be powered unless an engine is running.
Occasionally we connect AC to the aircraft on the line and this is when you need your wits about you, and at 4am this can be a problem.
Be safe guys and gals.