Illegal full autos have shown up. Google LA bank robbery and go from there.
First off, I believe that there is a distinction between rampages such as Aurora where the only goal is to kill and wreak havoc on innocent civilians and a bank robbery gone horribly wrong. Obviously havoc on police and innocent civilians alike was definitely the result of the North Hollywood shootout, but the goal was to steal money. They didn't draw stick figures, or write a letter telling of the impending carnage to a psychologist, or write a manifesto. They were criminals trying to steal money and had used the heavily armed tactic before. I couldn't tell you if they had purchased the guns legally or not, but it doesn't make much of a difference. People such as them, true criminals who want to rob and steal and kill if necessary to accomplish the aforementioned, or gang members, or neo-nazis, etc. would not be affected much, if at all, by a standard-capacity magazine ban, and I've said as much many times. I'm talking about psychopathic mass murderers such as the perpetrators in Tucson, Aurora, etc. In almost every instance they have legally acquired weapons (even the tear gas Holmes used is legal in Colorado) and use them to deadly effect. They don't have the black market access that true criminals have and rely on the available tools instead. Full-auto weapons are not available to those people and are consequently not used even though their killing potential is much greater. Ban further sale of standard capacity magazines and people like Jared Lee Loughner and James Holmes don't have them.
