What a sad sad day.
Even countries with gun control have instances like this (but they're arguably less frequent), and some countries with lots of guns have almost no problems like this at all (Switzerland for instance).
Just trying to imagine dropping a grade school kid off at school to find them dead in the afternoon from an insane thing like this I find that I can't do it, it is just too far from what I can still imagine. And I have a pretty rich imagination...
This world could be so nice, why does it have to be such a crappy place?
But when it comes down to it, if a crazy person can easily get a hold of a gun, then there will be more shootings. There are two requirements for shooting sprees, 1. Crazy person, 2. Easy access of guns. Try to limit both.