What we do not know is why a supposedly religious, 25-year FBI veteran with six children might have turned traitor. The Russians have a proverb for questions like this: "The heart of another man is darkness."
To understand Hanssen's motivation 60 Minutes II consulted his FBI boss and his alleged KGB superviser, as well as top spy recruiters, who used sex, money and friendship to turn patriots into traitors.
"He was a man in the shadows. He was always there," says David Major, Hanssen's former FBI boss. "And if you asked his opinion, it would be brilliant, but he wouldn't start the conversation."
For more than 10 years, both worked in FBI counter-intelligence, as America's spy catchers.
Major's job at the FBI was to find the moles. "It was my job to look around our entire nation as well as the FBI," he says.
Was Hanssen ever on his list of possibilities?
"He would never would've popped up," Major declares. "This was not a money man; it's a man who wore the same suit all the time, sometimes the same tie all the time."
"As a person he would've been the one you wanted inside your inner sanctum," Major adds. "He was that good; he was that smart."
In a profession where secret information is shared only on a need-to-know basis, Hanssen was entrusted with nearly everything. His job was to analyze all the intelligence. He knew the spies, the codes and the surveillance systems.
"These are the crown jewels," says Major. To lose all that from one of your own is a painful process, he adds.
Take the two U.S. spies in Russia who were Russian citizens working as double agents. Hanssen allegedly confirmed their identity; the KGB arrested them, and they were executed.
The FBI says Hanssen was paid $600,000 for his actions, but over 15 years that comes to $40,000 a year.
Hanssen had no love of money and no love of the Soviets, according to Major. "Not only would he talk about them operationally but he was a religious person," he says. "He would put it in a religious context. He would say that (the) Soviet Union is bound to fail because...because they're run by communists. And communists don't have God in their life."
So how does Major explain Hanssen volunteering to be a Russian agent? "I've been thinking about that since the first time I saw his name on the computer when it first came up, and I felt like I got kicked in the stomach," Major says. "I could see his mind saying, 'I am sitting in this meeting and they're discussing how to catch spies, how to find people who are agents, and I'm the one they really want, and I'm right next to them.'"
That could have been an intellectual rush for Hanssen, Major says. "But to do that he had to compromise things that we stand for."
"He was able to cross that line; the rest of it just became the game," Major says.
Hanssen was also allegedly employed by the head of Soviet counter-intelligence, Leonid Shebarshin, the last director of the Soviet KGB.
"If you look carefully at the background of...our traitors, you'll find that they were betraying their fellows even when they were in kindergarten," says Shebarshin, who in the 1980s led the elite branch that oversaw double agents, including Hanssen, Ron Pelton of the National Security Agency and CIA turncoat Rick Ames.
"Traitors are not made, says Shebarshin, who lives in Moscow. "They are born. But it depends upon the circumstances and surroundings, whether the seeds of treason produce bloom or they just stay repressed."
Money often helped, but "not only money, sympathy," Shebarshin adds.
For example, Ames liked the people that he worked with at the KGB, according to Shebarshin. "For me, he was not a traitor. He was my comrade. He was my colleague. He was a person who was trying to help my country. And to hell with your country."
Gennadiy Vasilenko, a KGB recruiter who worked in the Soviet embassy in Washington in the '70s and '80s, thought of himself as a patriot, he notes. "The United States of America was the enemy No. 1."
Most of Americans who became double agents and worked for the Soviets were motivated "just for the money and the dissatisfaction with their bosses, with their lives, with their wives," Vasilenko observes.
Jack Platt, a CIA recruiter in Washington who enlisted Russians to work for the United States, says the motives of Russians were entirely different. "In almost 65 percent of the cases the prime motivation...was revenge," Platt says. "Revenge for a...true wrong, or a perception in his or her head that something terrible had been done to him or her by that system."
Platt also cites the thrill of the game: "It's a very dangerous game, mind you, but there's also a great deal of thrill about it."
At that time, Platt and Vasilenko were working in Washington trying to recruit each other. For years they cultivated a friendship, going to ball games and meeting each other's families. Once Platt tried to recruit Vasilenko with a briefcase of cash. "I just asked for 20 bucks to pay for the...lunch, for the beer," Vasilenko says.
Platt says he was never tempted. "I once said to Gennadiy, what are you going to offer me? Five hours in a bread line? Nine square meters of living space in Moscow?"
They didn't succeed in recruiting each other but their friendship deepened. They met regularly, until one day Vasilenko disappeared. He had been ordered to Havana for what he thought was going to be a routine KGB meeting in an apartment building. On the veranda two men jumped on him, broke his arm and head, and he was accused of treason, Vasilenko recalls.
Vasilenko was thrown into Moscow's Lefortavo prison, where traitors are executed in the basement. "The prisoner is merely led down a darkened corridor where the lights are very dim," Platt says. A series of niches line the corridor, and in one stand two executioners. "As the prisoner is escorted by one of the niches, either one or both step out from behind the niche and put a bullet in the back of his head."
Expecting to die, Vasilenko wondered who had accused him and why? That was 13 years ago and he never knew the answer - until now. In an affadavit, the FBI says Robert Hanssen told his handlers that a KGB officr, with the code name M., had been meeting with a CIA agent.
"M." was Vasilenko, Platt says, adding that Hanssen turned Vasilenko in. "I now know that," Platt says. "And so does Gennadiy."
The CIA now believes the KGB agent that Hanssen refered to as "M." was Vasilenko.
But Hanssen was wrong about Vasilenko. According to Platt, Vasilenko had met with Platt but he wasn't a spy. "And if anybody should know, it should've been me."
Vasilenko could be considered an innocent victim of Hanssen, according to Platt. "He very nearly lost his life as a result of the betrayal of trust of Hanssen."
With too little evidence, Vasilenko was released after six months.
The same is not likely for his alleged accuser. The FBI says its evidence includes original copies of letters between Hanssen and the KGB. Where did the FBI get those letters? Most probably a mole. If Hanssen was a spy, it seems he planned for everything except a double agent like himself in Russian intelligence who would one day betray him.
"He was the master spy, the perfect spy, the Le Carre perfect spy," Major says. "And that means to be the perfect spy, you have to be the perfect spy for a long period of time. Not just once. And the longer he does it, the better the rush."
In one letter to the KGB, Hanssen allegedly wrote, "Would appreciate an escape plan. Nothing lasts forever." That was 15 years ago. The day he was arrested Hanssen was weeks from retirement. He would never meet the man who employed so many American spies.
The Cold War has ended but the spying continues. "What I managed to do was not demolished, was not swept away," Shebarshin says. "The service is alive and kicking and maybe even biting," he says laughing.
To the Americans who helped the KBG, he says, "Many thanks, ladies and gentlemen. I appreciated your efforts. And I am grateful to you."