In the US these criminals seem to be very careful about choosing the place to commit their crime. They choose places where they can be almost certain that there will be no effective (read: firearm) opposition, a resistance free zone so to speak. They don't like to fight. They like to kill. If effective opposition is in the offing they kill themselves or give up. With that in mind, it doesn't matter at all what kind of firearm they have for they plan that they will have the only one.
If they err in that, like the criminal in the mall in Oregon, or the criminal at the theatre in Texas, they fail.
Bookmarks