And I think you're missing the point. Absent a total ban on citizens of good standing possessing guns inside (including administrators in this case, or, say an arms locker in the teacher's lounge), the duo wouldn't have had free reign as the police cowered outside (experience shows teachers and administrators are a lot more serious and brave about protecting their charges than the local police were that day).

To take another example, the Colorado theater shooter could have gone to closer or bigger ones, but just happened to pick the one that was so ... severe about being "gun free" it insisted off duty police hired as security guards go unarmed. It was gun free, alright, until he showed up.

One correction to this pattern: the Arizona Congresswoman shooting, where an armed citizen showed up as the shooter was being restrained by people there, but one of them in the line could have been legally armed.