i wonder if any part of the plan (or his mindset) had to do with being under-gunned compared to the shooter. He had to have been wondering if the shooter had a rifle and if he should wait for better-armed backup to arrive before engagement.
A properly prepared plan would have addressed the above situation in simple terms. "...if an active shooting is taking place inside the school or on it's grounds, the armed, on-duty LEO will immediately address the situation by doing the following: _______". If it gets too much deeper than that, then I know an old retired Marine who either can write a proper plan for them or tell them how to do it.
Unless you happen to see with your own eyes as the bad guy is going in, there is no way to foresee what weaponry and equipment the bad guy may have. You also don't know if he has back-up in place or not. You don't know much of anything in a situation like this except that there is gun fire where it isn't supposed to be. So Whattya ya gonna do? Holler at him and ask?
"Hey! Hey! Yeah you...bad guy...yeah, I'm talkin' to you! Hey, would you please tell me what kinda guns and stuff you have and if you have any other guys in there with you helping you kill kids and teachers before I decide if I'm gonna do my job or not?"
NO. Either you respond to the threat immediately, (as that is part of the job and you knew the risks when you took it) OR you wait for back-up/negotiators to arrive. Again, if they did not have a plan in place, with specific, simple instructions on how to react, then they have a serious leadership problem on top of what appears to be an issue with chickenshit-itus in the ranks.
As has already been said, many of us do not know what we would have done in this situation, but I damned sure do. The minute I clocked in, as it were, I would be in Condition Orange until I clocked out, at the least. Sure, the odds of something like this happening to you are very slim, but you don't get old in this type of profession or environment by being careless and not paying attention. And the damn minute I heard gunfire, if not before, I would have been all over that punk with every bit of firepower I had at my disposal and then some, despite any BS about back up. Waiting to engage the enemy in this situation is wrong, stupid and defeats the purpose. The armed guard becomes a talisman, a visual deterrent, if that, and nothing else. The only way to defeat and maybe survive an ambush like this is to charge into it with maximum violence NOW. An old saying in the Marine Corps is this:
"A decent plan, violently executed with maximum force RIGHT NOW beats the hell out of a perfect plan...executed later". If someone accepts a position like this, they better be prepared to run to the sound of gunfire RIGHT NOW or they are in the wrong job and I bet they already know it.