Galt-in-Da-Box thinks these kinds of scenarios - as well as school shootings, "Bubba-'bama" rampages and the like - all make the case why the Militia Clause in the Bill of Rights should be enforced.
You see, if we actually meant what we said in the Second Amendment, it would be MANDATORY that the head of every household own, be trained in the use of and ready to use at all times, a pistol, shotgun &/ rifle of their choosing. Switzerland has done this for centuries now, and has never been conquered. I also imagine the incidents of "whack-job shootings" like this are rare & far-between there: If you are surrounded by folks who can and will throw down if you start some shit, it tends to add a moment of pause to the situation.
Code Name Insight offers some tips for dealing with the results of our effeminized, excuse-making culture of enabling gun-violence through "safe"-zones that should be valuable and fill the gap til we get with the program.