One revelation of the Venona project intercepts is that many Americans who spied for the Soviet Union were never prosecuted. To do so the government would have to reveal what it knew. On 29 May 1946, Federal Bureau of Investigation (FBI) Director J. Edgar Hoover sent a high administration official a memorandum reporting "an enormous Soviet espionage ring in Washington." Undersecretary of State Dean Acheson was (falsely) at the top of the list. Truman distrusted Hoover and suspected Hoover of playing political games. Acheson's inclusion at the top of the list automatically discredited other accusations which were on target, Alger Hiss and Nathan Gregory Silvermaster. [http://www.fas.org/sgp/library/moynihan/hoovlet.html] In late August or early September 1947, the Army Security Agency informed the FBI it had begun to break into Soviet espionage messages. Truman had never been told of the existence of the Venona project, and always insisted Republicans had trumped up the loyalty issue for political gain.