A gunman killed 10 people in Alabama before fatally shooting himself. Here is a glance at some of the worst U.S. mass shootings in recent years:
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, Nebraska at a Von Maur store in the Westroads Mall, killing eight people before taking his own life. Five more people were wounded, two critically.
Oct. 7, 2007: 20-year-old Forest County, Wisconsin Sheriff's Deputy Tyler Peterson went on a shooting rampage at a Crandon home where seven young people had gathered for pizza and movies. Peterson killed six and injured the other before fatally shooting himself.
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.
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.
Dec. 26, 2000: Software tester Michael McDermott, 45, killed seven people at a Wakefield, Massachusetts, Internet consulting company, Edgewater Technology Inc.
Nov. 2, 1999: Copier repairman Byran Uyesugi, 40, fatally shot seven people at Xerox Corp. in Honolulu, Hawaii.
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.
July 12, 1976: Edward Charles Allaway, a custodian in the library of California State University, Fullerton, fatally shot seven fellow employees and wounded two others.
Aug. 1, 1966: Charles Whitman opened fire from the clock tower at the University of Texas at Austin, killing 16 people and wounding 31.
Compiled by AP Researcher Julie Reed