I'm gonna chime in here. A thorough mental health check might have caught this troubled individual... or maybe not.
I think certain things can be done from a medical standpoint. ie: Are you diagnosed with depression? Maybe you should be asked to turn your guns in until the doc clears you.
Troubled/violent divorce? Maybe you should be required to turn your weapons in until you completed a few therapy sessions and the shrink clears you up.
Obviously, I understand not everybody will agree, and it certainly might not prevent every incident, but I get the feeling we're not taking mental health seriously enough, and we can be much more pro active about it.