A young marcher holds an antigun sign while participating in a rally and march across the Brooklyn Bridge on Jan. 21, 2013, with One Million Moms for Gun Control, a group formed in the aftermath of the Newtown tragedy.

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On Jan. 4, 2013, Gabrielle Giffords visited the families of the victims of the Newtown, Conn., mass shooting that, weeks earlier, had claimed the lives of 20 first-graders and six educators at Sandy Hook Elementary School, along with that of the gunman's mother.

In the two years since Jared Lee Loughner opened fire on the former Arizona representative and her constituents, shooting sprees had killed six at a Wisconsin Sikh temple, 12 at an Aurora, Colo., theater, four at a Carson City, Nev., IHOP Restaurant and seven in Grand Rapids, Mich. The attacks had also wounded many others. (And that's just a partial list of mass shootings in the U.S.)

Giffords, a moderate Democrat and gun rights advocate, and her husband, astronaut Mark Kelly, launched the organization Americans for Responsible Solutions to push for "responsible changes" in gun laws, countering the hard-line stance taken by the American gun lobby and the National Rifle Association (NRA). The NRA attributed the Newtown shooting to violent films and video games, and argued for armed guards in schools [sources: Kucinich; Lichtblau and Rich].

Tragic events spark fear and outrage, drive up gun sales and, conversely, inspire calls for expanded (or better-enforced) gun control [source: Ingram]. Congress passed the Gun Control Act of 1968 following the assassinations of Robert F. Kennedy and Dr. Martin Luther King Jr. The Brady Act, which requires background checks by licensed dealers (but does not apply to gun shows), arose from the 1981 assassination attempt on Ronald Reagan [sources: ATF; Hennessey and Mascaro; The New York Times]. The act is named for James Brady, Reagan's press secretary who also was injured in the attempt and went on to become a gun control advocate.

But as of January 2013, the possibility of legal reform following Newtown remains unclear, and the composition and effectiveness of such laws remains hotly debated.

One commonly proposed gun law reform involves banning assault weapons such as the popular AR-15, the semi-automatic rifle used in the Newtown and Aurora killings. The Clinton administration's Federal Assault Weapons Ban lapsed in 2004, and attempts to revive the measure have failed, due to both divergent views and the difficulty in codifying a workable and non-exploitable definition of "assault weapon" [sources: Haas; Kucinich; Lawrence; New York Times].

Public support for such a ban has flip-flopped. According to a post-Newtown USA Today/Gallup survey, while 58 percent of Americans supported tighter gun laws, the majority opposed banning "semi-automatic guns known as assault rifles" [source: Walsh]. Gallup asked again in January 2013 and found that 60 percent would be in favor of such a ban [source: Saad].

In the U.S., the gun control debate comprises strongly held views about constitutional law, the rights of the individual, the role of the state and the best way to keep society safe. But it also encompasses an important practical question: Do countries with stricter gun laws experience less crime or fewer homicides?

The answer is anything but simple.