So many opinions about what can be done to stop monsters and no solutions. The fact is that monsters have existed since the beginning of time and they always will. As years go by, monsters evolve into the kind of scumbag that murdered those kids. Hitler is a good example of a 20th. century monster who disarmed his citizens.
The point is that there is no solution. A monster determined to take lives, and sacrifice his own, cannot be stopped. Not even by armed guards (unless it's a high profile politician).