It's called re- creating the scene. It happens at work ALL THE TIME. You have a work related accident, you don't get the person who got hurt to stand around for pictures, you send him to medical to get checked out. But it has to be documented, so you re create the scene later and take pictures of that for documentation purposes.
I'm not saying this particular incident is valid, but a combination of what has been mentioned in this thread already seems like it could have happened. A combination of a pistol with no external safety, a holster not designed for that particular pistol which did not adequately cover the trigger guard, and something was used on the leather to make it extremely flexible and pliable to the point of moving exactly where it didn't need to be. Several factors were at play here.