The shooter was walking around trying to shoot anyone he could. Anyone within shooting distance of this guy was already in grave danger.
The scenario that you describe just is not plausible. If there were students that could be caught in a cross fire, they would have already been targets.
And the chances of someone a floor above, a floor below, or outside being hit is minuscule compared to the likelihood of the shooter being able to walk to the next room and kill people hiding inside, if given time to do so.
This explains why the psycho thug stayed in school so long:
https://twitter.com/TheLastRefuge2/status/966854970594287616
The shooter was spending enough time in each room, to shoot a number of people. Some of those people survived. Who’s to say they would have if an officer charged in and a gunfight ensued.
Yes, perhaps the officer would have prevailed. I can see some rather clear reasons why that might have been next to impossible, but let’s say he did save kids.
What happens if he goes in, the crossfire winds up killing five more, and the officer dies also? What would that have accomplished?