How the FBI Tracked Robert Hanssen

Feb. 20 -- Accused spy Robert Hanssen was arrested under dramatic circumstances on Sunday, but the FBI's investigation of him involved months of less glamorous legwork.

Concluding a four-month inquiry, federal agents nabbed Hanssen conducting what they say was a clandestine "dead drop" in the woods of suburban Virginia on Sunday evening. Hanssen, a 56-year-old counterintelligence specialist, was in the process of giving information to his Russian contacts in exchange for $50,000 in cash, FBI Director Louis Freeh said today.

The arrest was the culmination of a period in which the FBI monitored Hanssen extensively, using some of the most powerful surveillance techniques it could muster in order to build a case against him.

Authorities say the FBI operation was made trickier by the fact that a number of Hanssen's colleagues were involved in the investigation — and that Hanssen had a habit of checking FBI records in an ongoing attempt to see if his activities and communications were being watched.

"He constantly checked FBI records for signs that he and the drop sites he was using were being investigated," Freeh said at an afternoon news conference.

Key Break Led to Inquiry

Intelligence experts say Hanssen was so careful, and positioned so well at the FBI, that the agency may not have caught on to his activities without outside help.

"He didn't make any slip-ups," says Vincent Cannistrano, the former CIA director of counter-terrorism who is now an intelligence consultant for ABCNEWS. "He was identified through tips from penetration of Russian intelligence."

Freeh alluded to this today, saying the Hanssen investigation "was conducted by the FBI in partnership with the CIA, the Department of the State and, of course, the Justice Department," and that "because of these coordinated efforts, the FBI was able to secure original Russian documentation of an American spy who appeared to be Hanssen."

Specifically, the FBI managed to get possession of letters written by Hanssen and sent to his Russian contacts, Freeh said. The FBI chief quoted from them during his news conference.