Circumstances behind the shooting I guess is what I am asking. What motivated this guy to do what he did?
I apologize - I did not intend to nit-pick at your post. I thought the question of circumstance was relevant, in that focusing on the specific moment, one may lose sight of the bigger picture.
It's been my experience, when people lose their sheite, the provocation came long before, and is unrelated to, the triggering incident. Or, they are just plain evil -- which I suspect is the root cause in this case.