Further merely circumstantial background evidence is revealed in Jimmy Burns's 2009 biography of his father, spymaster Tom Burns. According to author William Stevenson in "A Man called Intrepid", his biography of Sir William Samuel Stephenson (no relation), the senior representative of British Intelligence for the western hemisphere during the Second World War, Stephenson postulated that the Germans knew about Howard's mission and ordered the aircraft shot down. Stephenson further claimed that Churchill knew in advance of the German intention to shoot down the aircraft, but allowed it to proceed to protect the fact that the British had broken the German Enigma code. Former CIA agent Joseph B. Smith recalled that, in 1957, he was briefed by the National Security Agency on the need for secrecy and that Leslie Howard's death had been brought up. The NSA claimed that Howard knew his aircraft was to be attacked by German fighters and sacrificed himself to protect the British code-breakers.