Here is a glance at some of the worst U.S. mass shootings in recent years:
Nov. 5, 2009: The Army says 13 people were killed and 30 wounded in a shooting rampage at its Fort Hood base in Texas. The suspect in the shootings, Maj. Nidal Malik Hasan, was wounded and is hospitalized.
April 3, 2009: A 41-year-old man opened fire at an immigrant community center in Binghamton, N.Y., killing 11 immigrants and two workers. Jiverly Wong, a Vietnamese immigrant and a former student at the center, killed himself as police rushed to the scene.
March 10, 2009: Michael McLendon, 28, killed 10 people, including his mother, four other relatives and the wife and child of a local sheriff's deputy, across two rural Alabama counties. He then committed suicide.
Feb. 14, 2008: Former student Steven Kazmierczak, 27, opened fire in a lecture hall at Northern Illinois University in DeKalb, fatally shooting five students and wounding 18 others before committing suicide.
Dec. 5, 2007: 19-year-old Robert A. Hawkins opened fire with a rifle in Omaha, Neb., at a Von Maur store in the Westroads Mall, killing eight people before taking his own life. Five more people were wounded, two critically.
April 16, 2007: Cho Seung-Hui, 23, fatally shot 32 people in a dorm and a classroom at Virginia Tech in Blacksburg, then killed himself in the deadliest mass shooting in modern U.S. history.
Feb. 12, 2007: 18-year-old Sulejman Talovic killed five and wounded four at the Trolley Square mall in Salt Lake City, Utah. He was then shot and killed by police.
Oct. 2, 2006: Charles Carl Roberts IV, 32, shot to death five girls at West Nickel Mines Amish School in Pennsylvania, then killed himself.
March 21, 2005: 16-year-old student Jeffrey Weise killed nine people, including his grandfather and his grandfather's companion at home, and then five fellow students, a teacher and a security guard at Red Lake High School in Red Lake, Minnesota, before killing himself. Seven students were wounded.
March 12, 2005: Terry Ratzmann, 44, gunned down members of his congregation as they worshipped at the Brookfield Sheraton in Brookfield, Wisconsin, slaying seven and wounding four before killing himself.
July 29, 1999: Former day trader Mark Barton, 44, killed nine people in shootings at two Atlanta, Georgia, brokerage offices, then committed suicide.
April 20, 1999: Students Eric Harris, 18, and Dylan Klebold, 17, opened fire at Columbine High School in Littleton, Colorado, killing 12 classmates and a teacher and wounding 26 others before committing suicide in the school's library.
March 24, 1998: Andrew Golden, 11, and Mitchell Johnson, 13, killed four girls and a teacher at a Jonesboro, Arkansas, middle school. 10 others were wounded in the shooting.
Oct. 27, 1995: A one-time Army paratrooper killed a fellow soldier and wounded nearly 20 others in a sniper attack at Fort Bragg, N.C. William Kreutzer, who is serving a life sentence, wounded most of the soldiers as they left an athletic field.
June 20, 1994: Former airman Dean A. Mellberg sprayed a military hospital with bullets at Fairchild Air Force Base in Spokane, Wash., killing four people and wounding 23 others before military police shot him to death. Two of those killed in the five-minute rampage were therapists who had recommended Mellberg's discharge.
Oct. 18, 1993: A civilian Army base supply clerk killed his boss and two co-workers and severely wounded two others at the Training Support Center in Fort Knox, Ky. Arthur Hill then drove 40 miles to the Veterans Affairs Medical Center in Louisville, where he committed suicide.
October 16, 1991: George Hennard, 35, smashed his pickup truck through a Luby's Cafeteria window in Killeen, Texas, and fired on the lunchtime crowd with a high-powered pistol, killing 22 people. At least 20 others were wounded.
Compiled by AP Researcher Julie Reed.