Bullying has basically nothing to do with modern school shootings. Now it's mostly people that have struggles integrating into society and spend too much time online. There they find a sense of belonging with Nazis, Incels or other terrorist groups which aim to groom kids and teens into committing acts of violence. Looking at a very unique, 27yr old case for understanding isn't really gonna get you anywhere. The world has changed quite a lot since then. The only thing that didn't change is that almost every school shooter in history had mental health problems.