Their perception is that everyone in that group did hurt them. School shooters frequently blame everyone in the school for not helping them, and for having a

Their perception is that everyone in that group did hurt them. School shooters frequently blame everyone in the school for not helping them, and for having a higher social status than they do. I think their motivation is to flip the social hierarchy so they are at the top, and to punish people they think have wronged them (i.e. basically everyone). The fact that it strikes fear into the rest of the nation is ancillary. They're usually more interested in the notoriety they gain than trying to create some kind of policy change.