The only thing "routine" about these events is that the ROUTINELY occur in designated gun-free zones, where the shooter is free to execute as many victims as possible with no fear of interruption by armed citizens.
When I heard about it yesterday, I predicted two things to my wife. First, there would be some mental disorder, likely known to friends, parents and in most cases authorities, to include teachers, doctors and the like. And second, even in a rural area, the killer found a no gun zone. Crazy people aren't necessarily stupid.