The only clear message in this complex issue is that violent crime overall does not increase with the availability of guns, but gun-related violence does [sources: Kates and Mauser; Liptak; Luo]. In 1996, for example, you were far more likely to be shot to death in America than in any of 35 other wealthy nations, but you were also less likely to be the victim of murder, or of violent crime in general [sources: Killias, van Kesteren and Rindlisbacher].
Some opponents of gun control, including NRA Executive Vice President Wayne LaPierre, say, "The only thing that stops a bad guy with a gun is a good guy with a gun" [source: Lichtblau and Rich]. But at least one study has shown that defensive gun use succeeds only rarely, and that gun owners are 4.5 times more likely to be shot during an assault [source: Branas, et al.].
Firearms, it seems, are neither as much the cause of, nor the solution to, violent crime as they are cracked up to be.
Yet it is difficult to consider the victims of the mass shootings described above, or at Columbine High School (April 20, 1999) or the Virginia Tech campus (April 16, 2007), and not wonder if more might have lived if firearms regulations had been tighter -- or more tightly enforced.
Because of the gun show loophole, the woman who bought three of the four guns used by the Columbine killers was never prosecuted, despite making a "straw purchase" for two minors [source: Jefferson County Sherriff]. Virginia Tech gunman Seung-Hui Cho passed a background check to purchase his weapons after a state judge had declared him mentally ill [source: Schmidt and Savage].
In these cases, it seems likely that better controls could have saved lives. But to really limit mass shootings, societies must also find effective ways to identify and treat the mentally ill, and to limit their access to sensitive areas and weapons.
Although Jared Lee Loughner had no criminal record to prevent him from purchasing a gun, he exhibited numerous signs of being psychologically troubled [source: Anglen]. The same could be said for accused Aurora, Colo., theater gunman James Eagan Holmes, Carson City, Nev., assailant Eduardo Sencion and Norway massacre perpetrator Anders Behring Breivik [sources: BBC; Frosch and Johnson; Lewis and Lyall; Lovett; The New York Times]. Preventing violent acts like theirs will require understanding and defusing the pathology that drives them -- a feat far easier said than done.
Ultimately, like so many aspects of human nature, violence abhors simple truths. As long as mental illness, disparity, fear and hate exist, so too will crime, and until we can better identify and treat psychological disorders, we will likely produce people capable of the most atrocious acts.