Clyde Tolson, "Background Data Regarding Development of CG 5824-S [Morris Childs] as FBI Informant and his Subsequent Advancement to National Leadership Position in Communist Party USA," memorandum to J. Edgar Hoover, March 12, 1959, pg. 1. Published in "FBI SOLO Files - March 1958 to August 1960." Washington, DC: Federal Bureau of Investigation, August 2011; part 10, pdf pg. 1350.
