Now the answer has become clear: Because Aurora, Colorado already has strict gun control laws on the books that make it:Illegal to carry a concealed weapon, even if you're a law-abiding citizen. Illegal to discharge a firearm in public unless you are a peace officer.
Thus, any person who would have shot James Holmes and stopped the massacre would, themselves, have been arrested as a criminal!
"Crime rates alone of cities such as Chicago and Washington D.C. prove that gun bans only increase crime. The D.C. police response rate is eight minutes; most crimes are done in less than one. Gun bans create a trouble-free world for criminals considering no one can defend themselves."