“...heinous abuse cycle...”
Public schools are often scary Lord-of-the-flies environments, especially the huge suburban ones where the cool kid cliques reign supreme.
Hordes of adolescents in one large cohort is a recipe for trouble.
This is not to excuse the shooter, even if he was bullied; however, the parents and teachers and coaches often do nothing when they see bullying and abuse occurring.
Most of the kids who bully generally aren’t afraid of school discipline. That’s the real problem with bullying: it appears most of the actual bullies have become a law unto themselves.
This has to be taken a step farther.
Until the schools and the other students admit their portion of their responsibility for these events, and then move to correct the situation, nothing will get better.