My understanding is there was only one teacher, a guy (not too many guys on staff at most elementary schools) who was out in the parking lot and who called 911 about the shooter wrecking his truck in the drainage ditch in back of the school.
The shooter opened fire on the building from the parking lot before he gained access, not the action of someone who knew he could walk right in.
That same teacher, still outside, was apprehended as a suspect by the first SRO to arrive on the scene. At that point the shooter entered the building.
That's an assumption and not an answer.
I think when 20 kids get murdered in a fish bowl everyone has a right to real answers to real questions.
