Obama just got done making a speech where he said that this is about the guns, and that this needs to be made political, blah blah blah.
This is a perfect example of "private ownership of guns causes kids to be like this" ... simply being BS.
Having a screwed up world view, having no sense of how to lead an even slighly gratifying life without resorting to something like this in order to feel important, having media that dwells on and actively hypes this sort of thing ... those and a hundred other motivations spark this urge in a small group of weak minded fools. If they never could get around to getting their hands on firearms, they're a few minutes of web surfing and a couple of trips to some retails stores away from majorly lethal backpack pressure cooker bombs a la Boston, or a few chains and some gasoline away from burning a couple hundred people alive a la Bali, etc. The issue isn't the tools, it's the wanting to kill, and wanting to be known for having done it.
That there's four of them cooking up this idea takes all the fun out of the lecture about it being all about insufficient spending on healthcare. That they were planning something like this without already having a closet full of firearms capable of mind-control that mysteriously makes them want to do it takes all the fun out of "it's the NRA's fault." Where's the president, back on TV, explaining that this is all about parents raising some twisted kids? Nope, that's a politically incorrect value judgement about other people, and we can't have that.