The tapes released Monday in response to a Freedom of Information Act request by The Associated Press show the sleeper agents meeting handlers, receiving money and transmitting coded messages. The probe was known as Operation Ghost Stories, according to the documents.

Russia provided members of the ring with false identities, high-tech communications gear and middle-class lives in America, and told them to cultivate academics, entrepreneurs and policymakers.

But a high-ranking US mole in Russian intelligence ran the ring and it never stole any secrets. Ten spies were arrested in June 2010 and traded for four Russians convicted of spying for the West.