They knew someone is shooting up the school.
They knew the school was being shot up.
Did they know it was by some ONE?
If they did know it was a single gunman then the situation goes beyond cowardice and incompetence and into a complicity with evil.
I tell you truly that my purpose that day would have been to get inside that school and to the shooter(s). How I did so might have varied if I thought there were ten gunmen as opposed to one.
That being said I agree with you that I can’t understand how a man could stand at a distance hearing gunshots in a school.