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?
Switzerland is interesting in many ways, one of which is the degree to which the government is very close to a true democracy, the fact that they don't waste a ton of money on their defence (which has a lot to do with them being in a geographically special position) and in the way that they have guns but abuse is low.
The fact that this is very different to the situation in the US might hold some clues to what could be done about this.