Sorry, but I disagree. There is no such thing as objective evil. This is a person who did what he thought was natural and right given his beliefs and the way he was raised.
As long as we justify having irrational, extreme beliefs, we will have these situations, no matter how much we control guns or keep track of mental health records. The real problem is that we continue to justify insane beliefs because they fall under the umbrella of religion. And please don't tell me that this is only a few fringe crazy people who have nothing to do with the bulk of religious people. These "lunatics" are literally following the teachings of their religion, and all the "moderate" people are providing coverage for them by not openly rejecting those teachings.