A possible major cause of school massacres has not even been mentioned in the media. At least I have not seen it. I believe it has been a major factor in all such tragedies.
That factor is the prescribed pharmaceutical drugs being taken by the shooters.
As I recall, the shooters have mostly been disturbed individuals with some kind of mental or personality disorder, and they are also on some kind of pharmaceutical drug, such as for ADHD or ADD. Schools and some doctors seem obsessed with keeping these kids pumped up with some kind of drug, some with dangerous side effects.
As you may know, the word "pharmaceutical" comes from the Greek word phamakeia, which in the Bible is translated as witchcraft or sorcery. That is the spirit that is rampant in our society and schools today.
Pastor Carl Gallups addresses other major causes at http://ppsimmons.blogspot.com/2012/12/stop-madness-newtown-conn-where-is-your.html , an excellent and insightful video.
We have a sick society and some so-called doctors are making it worse. It is a sign of the times.