At the school district where I worked at, a disgruntled student took a rifle and started shooting rounds into the buildings. The police officer assigned to my school drove out there by himself to go find him. After the Columbine shootings, officers were just told to go in there and find the shooter(s) and not wait for back-up. Fortunately, the police officer found the disgruntled boy.
I'd rather take my chances with Chinese students than American ones. Here in China I get into a kid's face and they back down. In the USA you are not guaranteed that the kid will back down. That is why I quit teaching in the USA and came to China. I can't deal with the violent kids and a system that automatically, most often than not, takes their side.