Kamen met with Grigory Kheifets and Grigory Kasparov, KGB officers at the Soviet San Francisco consulate. On July 1, 1944 Kheofets received from Kamen classified information on the American uranium stockpile and departed three days later to the Soviet Union with the information.  Kaman was fired from the Manhattan Project in 1944 after security officers overheard him discussing atomic research with Kheifets.
- US House of Representatives, 80st Congress, Special Session, Committee on Un-American Activities, Report on Soviet Espionage Activities in Connection with the Atom Bomb, September 28, 1948 (US Gov. Printing Office) pp. 181, 182.
- Report of 11 January 1944, FBI Silvermaster file, serial 3378;
- “Comintern Apparatus Summary Report”;
- The Shameful Years: Thirty Years of Soviet Espionage in the United States, U.S. Congress, House of Representatives, Committee on Un-American Activities, 30 December 1951, 39–40.
- John Earl Haynes and Harvey Klehr, Venona: Decoding Soviet Espionage in America, Yale University Press (1999), pgs. 232, 236.