In 2002, two men who became known as the "Beltway snipers" -- John Muhammad and Lee Boyd Malvo -- went on a shooting spree across seven states and Washington, D.C., killing 15 people. In the Washington area, the snipers killed 10 people in 13 shootings from Oct. 2 to Oct. 22.
Sources: Washington Post, WUSA9, ABC 20/20, Fox News, CBS, FBI, Police Executive Research Forum, Legal files. Credit: Maria-Pia Negro and Colleen Jaskot/Capital News Service.