I just found out that the antidepressant "Effexor XR" has, since 2005, had listed as one of it's side-effects "homicidal ideation".
The term "ideation" means "the formation of thoughts or ideas". So "homicidal ideation" is the formation of homicidal thoughts or ideas.
This means that a side-effect of antidepressants is the formation of thoughts or ideas about killing people. Hmm. So given that every school shooter that I know of was on antidepressants (see: a partial list of school shooters on psychiatric drugs) and that this type of drug can cause homicidal ideation then the connection between the school shootings and psychiatric drugs becomes pretty obvious.