The University of Texas- Austin clock tower shooter, 25-year-old Charles Joseph Whitman, killed 16 and wounded at least 30 people from his perch above the university grounds.
John Hinckley Jr. tried to assassinate President Ronald Reagan in front of the Washington Hilton. Reagan's press secretary, James Brady, was wounded and paralyzed in the attack. The attack brought gun control to the forefront of the debate and was in part the reason that Reagan later endorsed the Brady Bill, which established a national system for background checks and a five-day waiting period after purchasing a handgun. The provision that compels state and local governments to perform background checks was declared unconstitutional in 1996. Getty Images
George Hennard, 35, drove a pickup truck into a Luby's cafeteria in Killeen, Texas, fatally shot 23 people and wounded more than 20 others before killing himself. AFP/Getty Images
Columbine High School shooters Eric Harris, left, and Dylan Klebold examine a sawed-off shotgun at a makeshift shooting range March 6, 1999, in Douglas County, Colorado. A month later, the high school seniors opened fire on students and teachers in classrooms, the cafeteria and the library, killing 13 people and wounding 23 others. Getty Images
On the Virginia Tech campus in Blacksburg, Virginia, 23-year-old student Seung-Hui Cho went on a shooting rampage, killing 32 people in two locations and wounding an undetermined number of others. Cho later killed himself. Getty Images
Army Maj. Nidal Hasan, 39, allegedly opened fire at a military processing center at Fort Hood, killing 13 and wounding 32 others.
Jiverly Antares Wong walked into an American Civic Association center, gunning down 14 people and wounding four.
Jared Lee Loughner opened fire on a "Congress on your Corner" event held by former Rep. Gabrielle Giffords. The attack killed six and wounded more than a dozen people including the congresswoman, who barely survived a gunshot wound to the head. Getty Images
James Holmes, 24, allegedly killed 12 people and wounded almost 60 others during a midnight showing of the Batman movie, "The Dark Knight Rises," at an Aurora, Colorado, movie theater. Getty Images
A man comforts a young boy after the funeral for Jack Pinto, 6, one of the children killed when Adam Lanza stormed their elementary school and claimed the lives of 20 children and six adults after killing his mother. Lanza turned the gun on himself as police closed in. AFP/Getty Images