I see no reason at all why certain institutions shouldn't have a key (code and hand print recognition) and police call release system for gun lock boxes strategically located around the site, to be opened by employees trained to shoot in the case of an emergency situation where an armed intruder NEEDS TO BE STOPPED QUICKLY.
To me, this is simple common sense. I am absolutely heartbroken by Friday's slaughter of the innocents. The defenseless are the ones who need measures of self defence. The knowledge that there are lock boxes with guns located in a school and employees there trained to shoot might also DETER maniacs from busting in like they own the place and there's nothing anyone can do about it. The predator does not want to become quick prey. It takes only one maniac with a gun to kill multitudes. As well it takes only one person with a gun to shoot down the maniac and stop the mass devistation from continuing. But if you have to wait for that person to come in from outside.... it just takes too long.