How about arresting him when he showed up for school with ammo in his backpack?
Exactly.
A kid with a past like that should have been flagged in a database that prevented him from legally purchasing any firearm.
Of course, that wouldn't have stopped him from stealing a gun and using it...or using a bomb or some other weapon for doing harm.
I wonder why a person would show up with a few bullets in his backpack? How did they know there were bullets in there? Maybe someone who hated him put them in there to get him in trouble. They probably turned him in too.