On September 16 , 2013 , the Washington Navy Yard shooting occurred when lone gunman Aaron Alexis fatally shot twelve people and injured three others in a mass shooting at the headquarters of the Naval Sea Systems Command ( NAVSEA ) inside the Washington Navy Yard in the Southeast quadrant of the city . The attack , which took place in the Navy Yard 's Building 197 , began around 8:20 a.m. EDT and ended when Alexis was killed by police around 9:20 a.m. EDT . It was the second-deadliest mass murder on a U.S. military base , behind only the Fort Hood shooting in November 2009
Fort Hood shooting
2009 Fort Hood shooting
History of Washington, D.C.