1954 United States Capitol shooting
On March 1, 1954, four Puerto Rican nationalists, seeking to promote Puerto Rican independence from the United States, attacked the United States Capitol. They fired 30 rounds from semi-automatic pistols onto the legislative floor from the Ladies' Gallery (a balcony for visitors) of the House of Representatives chamber within the United States Capitol.
Source: Wikipedia — 1954 United States Capitol shooting (CC BY-SA 4.0)