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 suspected lone gunman has been identified as Army psychiatrist Major Nidal Malik Hasan, one of the 30 injured.
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.
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.
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.