Hanssen seemed thoroughly shocked and surprised by his arrest. But he was not nearly as shocked as the FBI. When Hanssen's arrest was revealed last Tuesday, FBI Director Louis Freeh called his alleged double dealing the "most traitorous actions imaginable" against the U.S. and warned that the damage could prove "exceptionally grave." It was one of the worst failures of American intelligence ever and a brutal humiliation for the FBI, which had not caught on to Hanssen for 15 years. Says an investigator inside the case: "This guy almost committed the perfect crime."

The intelligence community has launched a deep probe into exactly what Hanssen may have turned over to Moscow during those years, but a colleague believes he "gave the whole bleeping thing away." Hanssen had extraordinary access to precious U.S. secrets invaluable to the intelligence services of first the Soviet Union and now Russia and delivered upwards of 6,000 pages of classified stuff into their hands. In the process, analysts believe he compromised every important human and electronic penetration of Russia for the past 15 years. A blue-ribbon panel has been set up to undertake a postmortem of the FBI, to determine how to thwart other moles. As Freeh admitted frankly, "We don't say, at this stage, that we have a system that can prevent this type of conduct."

Everyone who knows the dour-faced Hanssen professed astonishment that he could be one of the great spies of the age. What, we want to understand, makes a man betray, and how did he get away with it for so long? Here, from the 100-page affidavit filed by prosecutors and from Time's own sources, is the story behind the alleged case against Hanssen.

The Spy Who Loved Spying A good spy needs a good cover, and Hanssen had one of the best. He looked the quintessential suburban dad, devoted to his wife and six kids, working a government job to pay for a four-bedroom split-level house on a cul-de-sac in a modest Virginia neighborhood, Catholic school and college for the kids, and three aging cars. Neighbors often saw him walking through a neighborhood park at night, letting his dog romp, though he rarely stopped to chat. He piled the family into a van every Sunday for Mass at the same church FBI boss Louis Freeh attended. He and his wife Bonnie belong to the church's conservative Opus Dei society. Bonnie is a devout, spiritual woman, much admired among her neighbors for her sunny optimism and her skill at child rearing. If the reserved, aloof Hanssen was less popular, he was still regarded by those who knew him as a good father, good husband, good professional. And a good son. "He has always been very honest and upright," said his mother Vivian Hanssen, 88, reached by Time at her home in Venice, Fla. "I don't understand how he could be leading a double life. I hope there are extenuating circumstances."

Yet Hanssen was in the perfect position to spy on his country. For 25 years, he rose through the ranks of counterintelligence agents who toiled on the FBI's "Dark Side," as insiders call the highly secretive National Security Division. In 1978, when Hanssen was posted to the big New York field division, most rookie agents required to work counterintelligence hated the job. The hot career path lay in the dramatic bank robberies and Cosa Nostra cases of the criminal division. Intelligence surveillances took years, decades even, and seldom if ever resulted in actual indictments.

But Hanssen actually seemed to like the slow, intricate building of counterintelligence cases and was well suited to it. If criminal agents called the other realm "Sleepy Hollow," the NSD boys scoffed at their rivals as "knuckle draggers." As an agent who worked with Hanssen in the Soviet unit put it, "The counterintelligence agents read the New York Times, and the criminal agents read the Daily News. Espionage cases are the best cases in the world because they're very cerebral." So was Hanssen. He read voraciously, everything from spy novels to Marxist tomes to the richly detailed logs filed by surveillance squads overnight. "He really wanted to do counterintelligence work," says the agent. MORE>>