How Spies Are Caught Espionage is a high-risk criminal offense. The traitor must fear arrest for the rest of his or her life, as the statute of limitations does not apply to espionage. Former National Security Agency employee Robert Lipka was arrested in 1996 -- 30 years after he left NSA and 22 years after his last contact with Soviet intelligence. There are four principal ways by which spies are detected: Reporting by U.S. sources within the foreign intelligence service. Routine counterintelligence monitoring. Tip from a friend or spouse. Their own mistakes. U.S. Sources Within the Foreign Intelligence Service: Of the Americans who held a security clearance who have been arrested for espionage, about half were caught as a result of information provided by a defector from the foreign intelligence service, or a penetration agent or friend...