In case of all school shootings the SSRI antidepressants like Prozac, Paxil, and Zoloft or the amphetamine-type drugs prescribed for ADHD, like Ritalin were in play. The drugs have been well studied. They do, in fact, push people far over the edge, scramble neurotransmitter systems, and result in patients committing suicides and murders.
For example; the 1999 Columbine school shooting perpetrators were on Luvox, an SSRI antidepressant, which was taken off the market by its manufacturer several years later.