The Newtown killing of innocents was horrible. But most don't seem to notice that there was another crazy shooter who invaded a shopping mall in Clackamas Oregon a few days before the Newtown incident. The Clackamas shooter shot 3 victims (2 died, one young woman survived and is doing well). Why was this limited to three victims? The shooter was confronted by a legally armed citizen carrying a concealed weapon ... the shooter then turned his gun on himself, ending his killing spree.
The police did not arrive at the mall for several minutes, and had this armed citizen not been there, the shooter would likely have killed many more people (getting bigger headlines, etc.).