Shoot to kill?
As any cop will tell you, they do not shoot to kill. They shoot to stop the threat. That means putting bullets into the big center mass of the body, the chest. Putting bullets in chests is very likely to lead to death, but the goal is to stop what they are doing. Their death is merely a by product of that, not the “goal” per se. The proof of that is that when they are dumped, a professional department has it’s officers begin first air on the downed bandit.
To that end of stopping them, it’s chest and head.
There is no place in that business for leg shots and other lunacy. It isn’t even worth the risk. So essentially yes, it’s “shoot to kill”, even though technically that is not the goal.
BANG!
Resource officers armed and on campus help but a prospective shooter will know that he only has to get off a first shot to the officer and he gets free fire until the police arrive. One can kill many children in that 5-10 minutes. If he doesn't know who is armed he doesn't get that free first shot.