Two problems:
1) school police passing on troubled ute even after a lengthy trail of antisocial behavior.
2) F_I allowing troubled individuals to remain on the street in order not to lose their confidential informant status.
In both cases, you can be sure no intervention will take place until the unsub explodes.
Two examples of ignoring trouble coming. That Broward County Parkland high school shooter was heart breaking as it was horrific.