In 1954 , Puerto Rican nationalists opened fire on members of Congress from the visitors ' gallery , injuring five representatives . On March 1 , 1971 , a bomb exploded on the ground floor of the Capitol , placed by the radical left domestic terrorist group , the Weather Underground . They placed the bomb as a demonstration against U.S. involvement in Laos . On November 7 , 1983 , a group called the Armed Resistance Unit claimed responsibility for a bomb that detonated in the lobby outside the office of Senate Minority Leader Robert Byrd . Six people associated with the John Brown Anti-Klan Committee were later found in contempt of court for refusing to testify about the bombing . In 1990 , three members of the Armed Resistance Unit were convicted of the bombing , which they claimed was in response to the invasion of Grenada . On July 24 , 1998 , Russell Eugene Weston Jr. burst into the Capitol and opened fire , killing two Capitol Police officers . The Capitol is believed to have been the intended target of the hijacked United Airlines Flight 93 on September 11 , 2001 , before it crashed near Shanksville in Somerset County , Pennsylvania , after passengers tried to take over control of the plane from hijackers
United Airlines Flight 93
United Airlines Flight 93
United States Capitol