Well only one thing could make it go bang something pulled the trigger through the full motion of travel either single or double..
The single action with safety off in an improper holster can and does happen, those ambi safety's are notorious for catching on things and flipping off.HK usp and HK 45.
Easy to tell if it fired in the holster, and yes we will find out.
How do you establish intent?
Well when a naked man is chasing a woman down an alley with a butcher knife and a hard on, I figure he's not collecting for the red cross...Inspector H. Callahan