Fair enough. As I said, I don't know but I can speculate: for people who aren't crazy, shooting someone isn't a casual act. Survivors and relatives of survivors are generally more focused on grief than anger. Anger is usually just one phase of mourning and recovery, and perhaps it passes relatively quickly. So survivors don't have a big window of "opportunity" when they're inclined to shoot.

Other possibilities: someone HAS planned to try and abandoned the plan. Or someone still will try.