It's no secret that the Russians have long tried to plant "sleeper agents" in the US - men and women indistinguishable from normal Americans, who live - on the surface - completely normal lives. But what happens when one of them doesn't want to go home?

Jack Barsky died in September 1955, at the age of 10, and was buried in the Mount Lebanon Cemetery in the suburbs of Washington DC.

His name is on the passport of the man sitting before me now - a youthful 67-year-old East German, born Albert Dittrich. The passport is not a fake. Albert Dittrich is Jack Barsky in the eyes of the US government.

The story of how this came to be is, by Barsky's own admission, "implausible" and "ridiculous", even by the standards of Cold War espionage. But as he explains in a new memoir, Deep Undercover, it has been thoroughly checked out by the FBI. As far as anyone can tell, it is all true.

It began in the mid-70s, when Dittrich, destined at the time to become a chemistry professor at an East German university, was talent-spotted by the KGB and sent to Moscow for training in how to behave like an American.

His mission was to live under a false identity in the heart of the capitalist enemy, as one of an elite band of undercover Soviet agents known as "illegals".

"I was sent to the United States to establish myself as a citizen and then make contact, to the extent possible, at the highest levels possible of decision makers - particularly political decision makers," he says.

This "idiotic adventure," as he now calls it, had "a lot of appeal to an arrogant young man, a smart young man" intoxicated by the idea of foreign travel and living "above the law".

Media playback is unsupported on your device Media caption "This kind of double life wears on you"

He arrived in New York in the Autumn of 1978, at the age of 29, posing as a Canadian national, William Dyson. Dyson, who had travelled via Belgrade, Rome, Mexico City and Chicago, "immediately vanished into thin air", having served his purpose. And Dittrich began his new life as Jack Barsky.

He was a man with no past and no identification papers - except for a birth certificate obtained by an employee of the Soviet embassy in Washington, who had kept his eyes open during a walk in the Mount Lebanon cemetery.

Barsky had supreme self-confidence, a near-flawless American accent, and $10,000 in cash.

He also had a "legend" to explain why he did not have a social security number. He told people he had had a "tough start in life" in New Jersey and had dropped out of high school. He had then worked on a remote farm for years before deciding "to give life another chance and move back to New York city".

He rented a room in a Manhattan hotel and set about the laborious task of building a fake identity. Over the next year, he parlayed Jack Barsky's birth certificate into a library card, then a driver's licence and, finally, a social security card.

But without qualifications in Barsky's name, or any employment history, his career options were limited. Rather than rubbing shoulders with the upper echelons of American society, as his KGB handlers had wanted, he initially found himself delivering parcels to them, as a cycle courier in the smarter parts of Manhattan.

Image copyright Getty Images Image caption The young KGB agent arrived in New York in the late 1970s

"By chance it turned out that the messenger job was actually really good for me to become Americanised because I was interacting with people who didn't care much where I came from, what my history was, where I was going," he says.

"Yet I was able to observe and listen and become more familiar with American customs. So for the first two, three years I had very few questions that I had to answer."

The advice from his handlers on blending in - gleaned from Soviet diplomats and resident agents in the US - "turned out to be, at minimum, weak but, at worst, totally false", he says.

"I'll give you an example. One of the things I was told explicitly was to stay away from the Jews. Now, obviously, there is anti-Semitism in there, but secondly, the stupidity of that statement is that they sent me to New York. There are more Jews in New York than in Israel, I think."

Barsky would later use his handlers' prejudices and ignorance of American society against them.

But as a "rookie" agent he was eager to please and threw himself into the undercover life. He spent much of his free time zig-zagging across New York on counter-surveillance missions designed to flush out any enemy agents who might be following him.

He would update Moscow Centre on his progress in weekly radio transmissions, or letters in secret writing, and deposit microfilm at dead drop sites in various New York parks, where he would also periodically pick up canisters stuffed with cash or the fake passports he needed for his trips back to Moscow for debriefing.

He would return the to the East every two years, where he would be reunited with his German wife Gerlinde, and young son Matthias, who had no idea what he had been up to. They thought he was doing top secret but very well-paid work at the Baikonur Cosmodrome in Kazakhstan.

Barsky's handlers were delighted with his progress except for one thing - he could not get hold of an American passport. This failure weighed heavily on him.

On one early trip to the passport office in New York an official asked him to fill out a questionnaire which asked, among other things, the name of the high school he had attended.

"I had a legend but it could not be verified," he says. "So if somebody went to check on that they would have found out that I wasn't real."

Terrified that his cover might be blown, he scooped up any documents with his name on them and marched out of the office in a feigned temper at all this red tape.

Image copyright Walker, Joe C. Image caption The real Jack Barsky is buried in a Washington DC cemetery

Without a passport, Barsky was limited to low-level intelligence work and his achievements as a spy were, by his own account, "minimal".

He profiled potential recruits and compiled reports on the mood of the country during events such as the 1983 downing of a Korean Airlines flight by a Soviet fighter, which ratcheted up tensions between the US and the Soviet Union.

On one occasion, he flew to California to track down a defector (he later learned, to his immense relief, that the man, a psychology professor, had not been assassinated).

He also carried out some industrial espionage, stealing software from his office - all of it commercially available - which was spirited away on microfilm to aid the floundering Soviet economy.

But it often seemed the very fact of him being in the US, moving around freely without the knowledge of the authorities, was enough for Moscow.

"They were very much focused on having people on the other side just in case of a war. Which I think, in hindsight, was pretty stupid. That indicated very old thinking."

The myth of the "Great Illegals" - heroic undercover agents who had helped Russia defeat the Nazis and gather vital pre-war intelligence in hostile countries - loomed large over the Soviet intelligence agencies, who spent a lot of time and effort during the Cold War trying to recapture these former glories, with apparently limited success.

Barsky later found out that he was part of a "third wave" of Soviet illegals in the US - the first two waves having failed. And we now know that illegals continued to be infiltrated in the 1980s and beyond.

He believes about "10 to 12" agents were trained up at the same time as him. Some, he says, could still be out there, living undercover in the United States, though he finds it hard to believe that anyone exposed to life in the US would retain an unwavering communist faith for long.

He is scathing about his KGB handlers, who were "very smart" and the "cream of the crop" but who seemed chiefly concerned with making his mission appear a success to please their bosses.

"The expectations of us, of me - I didn't know anybody else - were far, far too high. It was just really wishful thinking," he now says of his mission.

On the other hand, the KGB's original plan for him might actually have worked, he says.

"I am glad it didn't work out because I could have done some damage.

"The idea was for me to get genuine American documentation and move to Europe, say to a German-speaking country, where the Russians were going to set me up with a flourishing business. And they knew how to do that.

"And so I would become quite wealthy and then go back to the United States without having to explain where the money came from. At that point, I would have been in a situation to socialise with people that were of value."

This plan fell through because of his failure to get a passport, so the KGB reverted to Plan B.

This was for Barsky was to study for a degree and gradually work his way up the social order to the point where he could gather useful intelligence - a mission he describes as "nearly impossible".

The degree part was relatively straightforward. He was, after all, a university professor in his former life. He graduated top of his class in computer systems at Baruch College, which enabled him to get a job as a programmer at Met Life insurance in New York.

Like many undercover agents before him, he began to realise that much of what he had been taught about the West - that it was an "evil" system on the brink of economic and social collapse - was a lie.

Image copyright Jack Barsky Image caption Barsky (fourth right) felt at home with co-workers at Met Life

"There was a way to rationalise that because we were taught that the West was doing so well because they took all the riches out of the Third World," he says.

But, he adds, "what eventually softened my attitude" was the "normal, nice people" he met in his daily life.

"[My] sense was that the enemy was not really evil. So I was always waiting to eventually find the real evil people and I didn't even find them in the insurance company."

Met Life almost felt like home, he says, "because it was a very paternalistic, 'we take care of you' kind of a culture".

"There was nothing like we were taught. Nothing that I expected. I wanted to really hate the people and the country and I couldn't bring myself to hate them. Not even dislike them."

But he was keeping a far bigger secret from his KGB bosses than his wavering commitment to communism.

In 1985, he had married an illegal immigrant from Guyana he had met through a personal ad in the Village Voice newspaper - and they now had a daughter together.

He now had two families to go with his two identities, and he knew the time would come when he had to choose between them.

It finally happened in 1988, when after 10 years undercover he was suddenly ordered to return home immediately. Moscow was in a panic, believing the FBI was on to him.

To do anything other than run as ordered - grab his emergency Canadian birth certificate and driver's licence and get out of the US - would be potentially suicidal.

He dithered and stalled for a week. Could he really leave his beloved baby daughter Chelsea behind forever?

But the KGB was losing patience. One morning, on a subway platform a resident agent delivered a chilling message: "You have got to come home or else you're dead."

Media playback is unsupported on your device Media caption The Americans producers: 'Here was someone who lived it'

It was time for some lateral thinking.

From discussions with his handlers in Moscow, Barsky had come to believe the Soviet hierarchy feared three things about America.

He already knew about their anti-Semitism and their fear of Ronald Reagan, who they saw as an unpredictable religious zealot who might launch a nuclear strike to "accelerate" the Biblical "end times".

But he also remembered their "morally superior" attitude to the Aids epidemic - their belief that it "served the Americans right" and their determination to protect the motherland from infection.

Barsky stalled a bit more and then hatched a plan.

"I wrote this letter, in secret writing, that I wouldn't come back because I had contracted Aids, and the only way for me to get treatment would be in the United States.

"I also told the Russians in the same letter that I would not defect, I would not give up any secrets. I would just disappear and try to get healthy."

To begin with Barsky lived in constant fear for his life, remembering that threat on the subway platform. But after a few months, he began to breathe more easily.

"I started thinking 'I think I got away with this.' The FBI had not knocked on the door. The KGB had not done anything."

He gradually let his guard down and settled into the life of a typical middle-class American in a comfortable new home in upstate New York.

While he had fallen for the American Dream and the trappings of the consumer society, he still had some conflicting feelings.

"My loyalties to communism and the homeland and Russia, they were still pretty strong. My resignation, you can also call it a 'soft defection' - that was triggered by having this child here. It was not ideological. It would be easy to claim that. But it wasn't true."

Playing at the back of his mind was always the question of whether his past would catch up with him. And, finally, one day, it did.

The man who exposed him was a KGB archivist, Vasili Nikitich Mitrokhin, who defected to the West in 1992 - after the fall of communism - with a vast trove of Soviet secrets, including the true identity of Jack Barsky.

The FBI watched him for more than three years, even buying the house next door to his as they tried to figure out whether he really was a KGB agent and, if so, whether he was still active.

The 'illegals' programme

Image copyright Getty Images

The Soviet Union began using "illegal" agents, living in Europe under false identities, as early as 1919

Unlike "resident agents", who are in the country legally as diplomats, they are not immune from prosecution if caught

The first illegal was sent to the US in 1921, according to the Mitrokhin archive

Famous illegals include Rudolf Abel, unmasked as a Soviet spy in the US in 1957, and Richard Sorge, who posed as a Nazi journalist in Japan during the war

In 2010, 10 Russian "sleeper agents" on a long-term mission to spy on US policy makers were exposed - including Anna Chapman (pictured)

In the end, Barsky himself gave the game away, during an argument with his wife, Penelope, that was picked up by the FBI's bugs.

"I was trying to repair a marriage that was slowly falling apart. I was trying to tell my wife the 'sacrifice' I had made to stay with Chelsea and her. So in the kitchen I told her, 'By the way, this is what I did. I am a German. I used to work for the KGB and they told me to come home and I stayed here with you and it was quite dangerous for me. This is what I sacrificed.'

"And that completely backfired. Instead of bringing her over to my side, she said: 'What does that mean for me if they ever catch you?'"

It was the evidence the FBI needed to pick him up. In a meticulously planned operation, Barsky was pulled over by a Pennsylvania state trooper as he drove away from a toll booth on his way home from work one evening.

After stepping out of his car, he was approached by a man in civilian clothes, who held up a badge and said in a calm voice: "Special agent Reilly, FBI. We would like to talk with you."

The colour drained from Barsky's face. "I knew the gig was up," he says. But with characteristic bravado he asked the FBI man: "What took you so long?"

He kidded around with Joe Reilly and the other agents who interrogated him, and tried to give them as much information about the KGB's operations as he could. But inside he was panicking that he would be sent to jail and that his American family, which he had been trying to hold together, would be broken up.

In fact, luck was on his side. After passing a lie-detector test he was told that he was free to go and, even more remarkably, that the FBI would help him fulfil his dream of becoming an American citizen.

Reilly, who went on to become Barsky's best friend and golfing partner, even visited the elderly parents of the real Jack Barsky, who agreed not to reveal that their son's identity had been stolen.

"I was so lucky and so was my family that the decision-makers were nice enough to say, 'Well, you were so well-established, we don't want to disrupt your life,'" he says.

"It required some interesting gymnastics to make me legal because one thing I didn't have was proof of entry into the country. I came here on documentation that was fraudulently obtained, so it took 10-plus years to finally become a citizen. And when it did, it felt good."

Image copyright Other Image caption Barsky's coveted American passport

Barsky is now married for a third time and has a young daughter. He has also found God, completing his journey from a hardline communist and atheist to a churchgoing, all-American patriot.

He has even managed to reconnect with the family he left behind in Germany, although his first wife, Gerlinde, is still not speaking to him.

"I have a very good relationship with Matthias, my son, and his wife. And I am now a grandfather. When we talk about things like Americans playing soccer against Germans, I say 'us'. I mean the Americans. I am not German any more. The metamorphosis is complete."

The final act in his story came two years ago when he revealed the secret of his extraordinary double life on the US current affairs programme, 60 Minutes.

He had long wanted to share his story with the world, but his bosses at the New York electricity company where he worked as a software developer were less than impressed to find they had a former KGB agent on the payroll, and promptly fired him.

Barsky says he has no regrets. He knows how fortunate he has been.

"This kind of double life wears on you. And most people can't handle it. I am not saying that I lived a charmed life but I got away with it.

"I am in good health. I have had some issues with alcohol that I have overcome and I got another chance to have a good family life. And another child. And I am finally getting to live the life that I should have lived a long time ago. I am really lucky."

Perhaps the supreme irony of Jack Barsky's story is that he was only able to complete the mission the KGB had set him - to obtain an American passport and citizenship - with the help of the FBI. He cannot resist a smile at the thought of telling his KGB handlers that he has not been such a failure after all.

"I wouldn't mind meeting one or two of those fellows I worked with and saying 'Hey, see I did it!'"

Deep Undercover - My Secret Life and Tangled Allegiances as a KGB Spy in America, by Jack Barsky and Cindy Coloma, is published next month

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