The man, named as David Sheldon Boone, was an analyst at the National Security Agency. He is accused of passing documents to a KGB contact at the Soviet embassy between 1988 and 1991 - the year he retired from the army and the Soviet Union ceased to exist.
The documents were said to divulge details of what the United States knew about deployments of Soviet forces and weapons, information that betrayed the extent and techniques of US surveillance.
According to US government lawyers, Boone, now 46, volunteered his services in 1988 by simply turning up at the Soviet embassy in Washington. He was said to be desperate for money after his marriage broke up and his entire army salary was allotted to his ex-wife. The KGB allegedly gave him $300 for the first document he offered, and a total of $60,000 over three years. He was transferred to a US field station in Augsburg,Germany, and maintained contact with his KGB handler, "Igor", for three years.
In 1990, Boone was transferred from his intelligence duties and lost security clearance because of concern about his debts, and opted for retirement.
Boone, who had married a German, remained in Germany in retirement. He was trapped by an FBI officer posing as a Russian agent who approached him in Munich about resuming his alleged espionage activities. He went to two meetings in London, and was then invited to Washington, where he was arrested.