The High School in question had 7 full time costumed govt employees tasked with security.
Hence the importance of letting the adult would-be targets arm themselves.
The guards are there for a lousy paycheck, and no bonus if they actually step in harm’s way. The attacker will of course avoid them.
The teachers ARE in harm’s way, should ham come. The first may have no warning; the rest will hear the commotion and have time (though little) to draw.
Incident shows the fallacy of paranoid imperative of disarming all.