These kids were described as unpopular, and no doubt they were picked on by other students. It occurs to me that the same students who are today on CNN describing these boys as crazy and deranged and innocently wondering why this happened, are possiblythe very same students whose abuse may have contributed to the violence. According to the press because of constant harassment, these boys were driven by hatred and banded together to form the Trenchcoat Mafia, a group where they could feel accepted. I don't think the feelings that these boys had are as distant from us as we'd like to think. The difference between these boys and average person is the way they choose to act on their anger.
People can be cruel and high schools are famous for their aggressively exclusive groups of friends.
A kid who has to deal with this outporing of hatred and disrespect everyday is very likely to want to lash back. Teachers can't always see 'warning signs' The buzz now is talk of prevention, of identifying the kids that are outcasts or troubled and helping them. There is a lot of rhetoric about having more people trained to notice the warning signs and counsel them. Many people think that teachers should be on the look out. What it takes is vigilant teachers.