None of the suspects, who allegedly served as undercover agents for Moscow's foreign intelligence service, was arrested until Sunday. But a close examination of court documents indicates that by mid-2006 investigators had already searched the homes of four of the couples, planted microphones in at least three of their residences, regularly reviewed their encrypted computer messages, and videotaped meetings where money and equipment were exchanged.  (Photos: Infamous spies throughout history)  So why hadn't any of the alleged spies been arrested earlier?  "There is always something else to be learned," said a senior law enforcement official.  Indeed, the investigation into the 11 alleged foreign agents appears to have been a case study in counterintelligence. As a matter of technique, the FBI and the CIA generally weigh the opportunity of gaining valuable counterintelligence against the danger of allowing subjects of interest to continue operating, lest they obtain U.S. intelligence or manage to flee.  In the Russian spy case, the counterintelligence gains could have included the names of Russian couriers and spy handlers, the names of Americans whom the Russians had sought to recruit, or knowledge of Russian espionage techniques and practices that could be employed in counterintelligence activities elsewhere in the world.  Already, the FBI has revealed enough information about the suspects to indicate that it may have gained valuable counterintelligence about Moscow's spy operations. According to a Justice Department letter filed in U.S. District Court in New York, for example, the FBI has acquired and decrypted more than 100 messages exchanged between one couple, Richard and Cynthia Murphy, and the SVR, the Russian spy agency. Only about 10 of those messages were described in the criminal complaint against the Murphys, who reside in New Jersey.  Separately, the Yonkers, N.Y., apartment of Vicky Peleaz, a columnist for New York's El Diario La Prensa, and Juan Jose Lazaro, a political science professor, was bugged in February 2002. Yet in court papers the Justice Department described only five conversations recorded inside the apartment over the intervening years.  (Interactive: The spy next door?)  The case against the suspects appears to have been built gradually over the years. One or another of the initial two couples that the FBI tracked led agents to the others, either when they met to transfer money or had exchanges to set up meetings. The search of one couple's home in 2005, for instance, led to the discovery on a computer of passwords permitting access to a Russian encryption software program involving "steganography," by which messages are concealed in otherwise unremarkable images. A year later, that discovery allowed investigators to reconstruct deleted steganography messages on the computers of two other couples.
The Russian spy case that exploded into public view this week was preceded by nearly a decade of cat-and-mouse activities with the FBI, according to court documents and an interview with a senior U.S. official familiar with the case.