Inevitably following a massacre people start talking about gun control, but I'm going to move away from that and toward something far more pertinent but rarely spoken of. When you have a naturalist's world view, you can see these things for what they really are, which is mental illness. People forget that your mind and personality comes from a biological organ, and it is susceptible to disease and failure just like the rest of the body. When you see the mind-- the soul, perhaps-- as an ethereal entity piloting a machine, you conclude that a mass killer is evil when he's really just sick. Sick people can't be reasoned with, and they need to be taken care of before these kinds of things will happen. The signs of sociopathy and psychopathy must be detected early, especially when they're children, lest we think of them as having simple personality defects to be grown out of in time.
The latest I've heard is that the mother of the killer knew right away that the perpetrator was her own son. I'm willing to bet she knew he had problems for a long time, but again, society doesn't take these things seriously because society has the completely wrong view of why these things happen. Let's recognize the facts: there is no soul, we are at the mercy of our brains, and sometimes our brains get sick. Let's do it right, and put one person in a hospital instead of a dozen in the morgue.