On September 17, the BOI released the contents of flyers found in a post office box in the Wall Street area just before the explosion. Printed in red ink on white paper, they said: "Remember, we will not tolerate any longer. Free the political prisoners, or it will be sure death for all of you." At the bottom was: "American Anarchist Fighters". The BOI quickly decided that the flyer eliminated the possibility of an accidental explosion. William J. Flynn, director of the BOI, suggested the flyers were similar to those found at the June 1919 anarchist bombings.