I get what you are doing here but I think you are misled. The police has a monopoly on violence to protect the state apparatus and the ruling class. Protecting normal citizens is a means to an end of that, it never was the goal. The US police originated in a force that brought back run away slaves. Are we talking about run away slaves? Is there private property at risk? Is the school shooter threatened any organ of the state? So why bother? TLDR ACAB

You mean without the strong police, there would be an upcoming rebellion by the schoolkids?