AT THE HEIGHT of the Cold War, during the winter of 1980, FBI agents recorded a phone call in which a man arranged a secret meeting with the Soviet embassy in Washington, D.C. On the day of his appointment, however, agents were unable to catch sight of the man entering the embassy. At the time, they had no way to put a name to the caller from just the sound of his voice, so the spy remained anonymous. Over the next five years, he sold details about several secret U.S. programs to the USSR.
It wasn’t until 1985 that the FBI, thanks to intelligence provided by a Russian defector, was able to establish the caller as Ronald Pelton, a former analyst at the National Security Agency. The next year, Pelton was convicted of espionage.