@farmerman,
Face it, the guy could have walked in with one of the little Ruger target pistols and five or six magazines, each with eight or ten cartridges, whatever those hold, and he could have had that in his pockets. It takes two or three seconds to change a mag in one of those, i.e. two or three seconds while kids are diving for cover and making easier targets of themselves.
That's a WMD which can be bought anywhere for two or three hundred dollars.