Executive Order 11669—J. Edgar Hoover
As a mark of respect to the memory of J. Edgar Hoover, it is hereby ordered, pursuant to the provisions of Section 4 of Proclamation 3044 of March 1, 1954, as amended, that until interment the flag of the United States shall be flown at half-staff on all buildings, grounds and naval vessels of the Federal Government in the District of Columbia and throughout the United States and its Territories and possessions. I also direct that the flag shall be flown at half-staff for the same length of time at all United States embassies, legations, consular offices, and other facilities abroad, including all military facilities and naval vessels and stations.
The White House,
May 2, 1972
Richard Nixon, Executive Order 11669—J. Edgar Hoover Online by Gerhard Peters and John T. Woolley, The American Presidency Project https://www.presidency.ucsb.edu/node/306978