Mayors Against Illegal Guns has a paper that’s worth reading here about the 43 incidents in which four or more people were killed with a gun between January 2009 and January 2013. A few notes:
In four incidents, the individual involved had a concealed-carry permit. This is striking — John R. Lott previously compiled a list indicating that 23 permit holders had committed any murder with guns between 1990 and mid-2008, which is a similar rate (around one a year) despite covering a much wider range of incidents. Of course, the overall low rate at which permits are revoked shows that permit holders are incredibly law-abiding; when one intends to commit murder, a lack of a concealed-carry permit won’t be much of a deterrent; many murders occur at home, where a permit isn’t even required; and Lott’s estimate indicated a murder rate 1/182nd that of the general population — but comprehensive data on murder by permit holders would be useful.
Only 28 percent of the incidents are known to have involved high-capacity magazines or so-called “assault weapons.” These incidents were more deadly than the others, but they include outliers such as Newtown and Aurora, and it does not follow from this correlation that banning these weapons would lower the body count.
Of the incidents that took place in public, nine occurred in places that were not “gun-free zones.” These include an incident in New York and one in Massachusetts, which are “may issue” states (meaning law enforcement may reject a permit application even if the person is not prohibited by law from getting one). Still, it cuts against claims that virtually all public shootings take place in gun-free zones.