Legislative reaction: Lawmakers announced several bills that would limit high-capacity magazines like those used in the Tucson shooting, as well as bills that would close loopholes in gun legislation relating to suspected terrorists and require background checks at gun shows. None of the legislation was enacted.
July 20, 2012 - Aurora, Colo.
Wounded: 58 James Holmes, a 24-year-old former doctoral student dressed as the Batman character "The Joker," allegedly opens fire in a midnight showing of "The Dark Knight Rises," in Aurora, Colo., killing 12 and wounding 58 others. Holmes used an AR-15 semi-automatic rifle, a 12-gauge shotgun and at least one of two .40-caliber handguns.
Legislative reaction: While the presidential campaigns of Obama and his challenger, former Massachusetts Gov. Mitt Romney, paused to pay tribute to the victims of the shooting and their families, the campaigns largely sidestepped the issue during the election. No legislation has been enacted.
Dec. 14, 2012 - Newtown, Conn.
Dead: 28, including the shooter Adam Lanza, a 20-year-old resident of Newtown, Conn., uses his mother's semi-automatic .223-caliber rifle to shoot and kill her in her home before heading to Sandy Hook Elementary School, where he guns down the school's principal, four other adults, and 20 children, all 6- and 7-year-olds. He was also found with at least two handguns.
Legislative reaction: Renewed calls for stricter gun legislation came about in the wake of the massacre. Obama vowed to support efforts by Sen. Dianne Feinstein, D-Calif., to reintroduce the assault weapons ban and asked Vice President Joe Biden to lead a group to examine U.S. gun policy -- including limits on high-capacity magazines, background checks at gun shows and limits on military-style weapons. Sen. Frank Lautenberg, D-N.J., indicated that he would once again introduce legislation to ban high-capacity magazines.
Internationally, however, several mass shootings have produced different legislative results.
March 13, 1996 - Dunblane, Scotland
Dead: 18, including the shooter
Thomas Hamilton, 43, wielding a gun, enters a school in Dunblane, Scotland, and shoots and kills 16 students and one teacher. The shooter then killed himself.
Legislative response: After the shooting, an inquiry called the Cullen Report was commissioned. A year later, legislators enacted two laws that effectively made private gun ownership illegal in the United Kingdom.
April 28, 1996 - Port Arthur, Tasmania, Australia
Martin Bryant uses a Colt AR-15 semi-automatic rifle to murder 35 people in Port Arthur, Tasmania. His attack is one of the deadliest in Australian history.
Legislative response: Conservative Prime Minister John Howard oversaw sweeping gun control reforms including all automatic and semi-automatic weapons. The Australian government also enacted a mandatory firearm buyback that led to the purchase and destruction of 650,000 firearms around the country.