I work at a high school of around 800 kids (5A school in Oklahoma, 6A is the largest). We have a hard point entrance. Always locked. The doors to the art building, gym and cafeteria? Always locked. Never unlocked. Not even now as school is out and admin is working. There are hundreds of cameras. If you get into the front door, there is a secondary LOCKED door. The front office has to let you in at all points.
We used to have a SRO in the front, officer from my town. We are getting a new one next year as well as a security guard at the gate again. The high school my girls went to (same town), it's even harder to get into.
There are ways to try and prevent these things as they play out. It won't stop all of them, but the DO stop them and have every year.
Until you throw out ideas, no need for you to participate in this IMO.