Bottled-up anger, mental illness, and alienation seem to be the common denominator (one or all three or many more) plus a sick need for attention. In all my high school years, we had one death from Russian roulette (risky but not to anyone but himself) and a hunting accident (think that guy lived), so all this is totally alien to me but having been around since it started, not new..
Kids think differently now. Plus they probably talk about more evil things than we would have thought of. Their entertainments have more evil elements in them. Clothing styles are unattractive and if they make the wearers feel good about themselves, I don't see how. I definitely think seeds are planted by sensationalizing these incidents in the news, not that I fault the news because we need to know what it going on and profiles of the perps. Our local paper had the Omaha incident placed at the top left, and published the photos when they came out. Then so many comments were so totally negative, they moved it off the front page of their website but kept it up.
This happens and you have to scroll way down on the left to see what they have on it. Plus they didn't open any of this one to comments.
There is a callousness in our society that makes it acceptable for people to make horrid remarks about a tragedy like this. A mental health professional on FOX put it well, I thought. He said something on the lines of people are so hurt these days that they retreat into apathy to keep from being hurt again. The problem with that is that the apathy keeps them from being able to empathize, and if you can't empathize, you can make awful comments about a tragedy. Or, on another level, walk into a mall and kill indiscriminately.