I don't know about school shootings specifically, but SSRIs have definitely been clinically proven to increase suicide in adolescents.

I'll have to use my Google-Fu to find out of the guy responsible for this is a quack or not. There's no link to the actual study.

PS. You can download some of their papers here: http://www.walshinstitute.org/researchstudies.html

PPS. The general consensus is that he's not a quack but that this needs a ton more research and the "5 distinct types" probably doesn't really fit.