The guy who shot up the MacDonalds was a professional welder who called the emergency mental health hotline the day before his rampage, but they never called him back. Autopsy showed he had high levels of exotic metals in his brain, a probable result of technical welding, that likely contributed to his mental breakdown. It didn't help that LE was initially dispatched to the wrong MacDonalds
I was a SWAT commander for years and we did much training for such events. The Columbine event changed the way LE should respond to active shooters. Uvalde didn't get the training.
It is good for responders to know the facilities where it might occur.
In recent years I taught a course for businesses and government on surviving an active shooter. In preparation I studied mass killer events over a 100 year period. There are some commonalities.
1. Active shooters generally do not expect to survive the event
2. There will be an LE response, nowadays usually within 10 minutes. The shooter when confronted by LE will likely be killed by police, or commit suicide. But 10 minutes is an eternity.
3. Those present inside the event stand a better chance of surviving the attack if emergency procedures and facilities design can slow his attack. Survive 10 minutes and you will probably survive the event.
4. Run, Hide, Fight is taught and has some merit. Running gets you out of the kill zone and spoils his aim. Hiding removes you as a visible target. Fighting is a last ditch response but may be your only recourse. Things like fire extinguishers, fire axes, chairs, etc may make a difference if you bring them with violence of action. Hiding under a desk is not a workable plan.
5. Active shooters do not expect armed resistance. It is why they choose soft targets where victims are unarmed. An armed person present who is capable dramatically changes the dynamics. Whether you choose to intervene depends on circumstances.
6. If you are the armed person present, speed, power, and accuracy will determine the outcome. You want to get inside his OODA loop if you can. The rule of 3's is usually in play (3 rounds fired, 3 yards, 3 seconds). All the esoteric tactical stuff aside, THERE IS NO SUBSTITUE FOR MARKSMANSHIP. I have hostage targets that we use for quick head shots on the timer. A lot of good shooters are shocked when they miss and hit the hostage. It is good to know the limits of your skills so you know what you need to work on. Consistently hitting an eyeball sized target at 3 yards is a step in the right direction.
7. We should all pray to never experience such an event.