Once you go beyond "gun" laws you can increase the count almost to infinity.
"Breaking and entering"? He broke the glass to open the door, that one's a give-away.
"Defiant trespass"? If the principal who confronted him managed to say "You can't come in here!" before he shot her, then his entering after he killed her was defiant trespass.
Does it matter, in comparison to 27 counts of murder? This is a gun board -- why don't we stick to the question as originally posed? How many GUN laws were broken?