If he was a felon, then their a fifth (and possibly sixth crime):
- Theft (presuming he stole the gun)
- Possession of a firearm by a felon
Plus the other four. Obviously, if he wasn't a known felon yet, these two don't apply.
My point was, he was a criminal before ever pulling the trigger. Having a gun in your hand on K-12 school property is a crime in itself in most states.

What is the point of rules that are not enforced?