All these twerps, puffing and posturing and bragging about what they would do are full of crap. There was a shooter in Tucson who hid in the Walgreens. We've heard similar with so many of these idiotic shootings. They're nothing but fierce little Mighty Mouse wannabes.
Its very likely there were other guns there as well. In this case, the cops were there within minutes, engaged the shooter within minutes.
The other excuse we hear is that mental illness is to blame. If that were true, there would be mass killings in every civilized country in the world. So far this year, 10 THOUSAND people have been killed by guns. What other country would put up with that?