[quote=scaredyclassic]…but…gosh…there’s lots of mentally ill people who don’t act liek this…[/quote]

No doubt. It’s only one factor.

Lots of people are mentally ill. Lots of people are socially inept. A smaller but still large number are both. And only a tiny percentage of those will actually lash out violently. Nonetheless, considering that most spree killers in this country these days are socially inept, it seems obvious that it’s an important factor. Which makes sense, given the toll that years of merciless social torture from your peers must take on a person.