In the farthest corner of a cobbled courtyard, at the top of a hill, up two flights of stairs in a 15th-century German castle, a handsome young professor is writing a book on Iraqi archaeology in the fifth millennium BC. In May of this year, when he was appointed professor of archaeology at Tubingen University in south-west Germany, he gathered his students around him and said, "I am Ricardo Eichmann. I suppose you all know the significance of the name Eichmann. Adolf Eichmann was my father. If you think that means I am a Nazi, then you had better leave now because I can assure you I am not."

Until two months ago, Ricardo Eichmann had lived in relative anonymity. Eichmann is to the German phone directory what Smith is to the British one and few would have suspected that the softly spoken 39-year-old academic was the son of the Nazi war criminal responsible for the mass deportation of Jews to the death camps during the Third Reich.

"Change my name?" he asks. "What would have been the point? You cannot escape from yourself, from the past."

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Ricardo Eichmann was born near Buenos Aires in 1955. His mother, Vera Eichmann, was 45. His father, Adolf Eichmann, alias Richard Klement, was 50. In hiding from Nazi-hunters, Adolf Eichmann changed his name but strangely never changed those of his wife and four children. It was this that led to his capture by the Israeli secret services in 1960.

Over the past months, since the local German press realised they had the son of one of the world's most hated men in their midst, Professor Eichmann has been pushed to recall the details of his early childhood, though he was only five at the time of his father's kidnapping and seven when Adolf Eichmann became the first and only man to be hanged in Israel.

"I remember him holding my hand and taking me to the bus stop. I remember him taking me into a sweet shop and buying me some chocolate. And I remember sitting outside on the step every evening thinking, when will my Daddy come home?"

But last month, Ricardo Eichmann was told that he had got his sequences of events wrong, that he never used to sit and wait for his father outside their house in Buenos Aires. Perhaps he had done that later, in Germany, when his father had been hanged and he still hoped he might come back. The man who corrected his childhood memories was Zvi Aharoni, the Israeli secret service agent who spent months observing the Eichmann family in Buenos Aires before kidnapping Adolf Eichmann, disguising him in an air steward's uniform and flying him to Israel.

Ricardo Eichmann met his father's kidnapper in a room at the Heathrow Hilton. "It was a very emotional meeting. People have asked if I feel anger towards him. I don't. Adolf Eichmann deserved to be brought to justice for what he did. I don't agree with the death penalty, but I can see why they did it at the time."

He pronounces his father's name as if he were talking of a stranger. "Adolf Eichmann," he says, "is a historical figure to me." But the historical figure left him with a disturbing legacy: a fatherless childhood, an adolescence filled with darkness and half-truths, and a lifetime label of "Eichmann's son".

Vera Eichmann left her two eldest sons in Argentina and brought Ricardo and his elder brother back to Germany to be educated. Money was tight - the widow of a Nazi war criminal was not entitled to a pension - so Vera's family helped financially, but emotionally Ricardo was on his own. "I knew my father was dead, but I didn't know how he had died. My mother kept all the newspaper cuttings about him under the sofa. I would creep under there and peek at them. I understood bits and pieces but not the whole picture. When I asked my mother, she would say, 'Lass das' - leave it. It was a taboo subject and stayed that way till my mother died two years ago."

Ricardo Eichmann has not shared his anguish with his brothers and has communicated with only one of them. "If you want to know what they think of me talking about this, you had better go and ask them," he says. One senses that he has dissociated himself from his siblings; later, seeing a picture of his elder brother Horst as a youth wearing an SS uniform, I understand why.

He envied other children whose fathers had been killed in car accidents or died of illness. At least, he says, they knew the truth. "When I was 13 or 14, I opened a magazine and saw a picture of - what do you call it in English?" He traces the shape of a noose around his neck. "Ah yes, the noose which hanged my father. Then I understood."

There is a silence. Professor Eichmann needs some fresh air. We walk down a slope towards the piazza. Over coffee, he says: "Once, at school, the history teacher started talking about an exam she had set on the Eichmann trial. Later she called me in. She said she hadn't meant to offend me. She hadn't realised I was in the class. I remember always going bright red when people mentioned Nazis and SS men."

I am struck by Ricardo Eichmann's apparent lack of anger. He wasn't angry with his father's kidnappers, he wasn't angry with the Israelis for hanging him. Was he not even angry with his mother for not explaining things to him?

"Look," he says. "I am bitter about the fact I had no father. I am furious about the horrors of the Holocaust. And it would have been better if she had talked to me. I wanted to challenge her, but I saw her inner turmoil. I loved her and she loved my father. What was I supposed to do?"

Professor Eichmann's facial muscles begin to twitch. "I know now that pain comes from not knowing. That is why I am not afraid to confront the truth. I always wanted to know. I went to see the deportation orders, black on white, that my father had signed. I never wanted anyone saying that I didn't believe what he had done."

Since Ricardo Eichmann's heritage has become public knowledge, he has received calls from neo-Nazis, expecting to find a sympathetic ear. "A few weeks ago, I got a call from Australia, from a man who said, 'Eichmann was OK.' I said he most certainly was not."

On the other side of the coin are the Holocaust survivors who believe that Ricardo Eichmann "has it in his blood", "it" being a genetically transmitted racism. I tell him that my grandmother, a German Jewish refugee, is angry and hurt that I am interviewing him. For the first time in three hours his face registers pain.

"I know there are people who feel like that about me. What can I do? Perhaps it is my fate. You know when the article came out about my meeting with Aharoni, they did a survey in Israel. For every three people who were positive towards me, there was one who thought I must be a Nazi. They were mostly old people who had been through the atrocities who felt that. I would like to go to Israel, but I don't want to offend anyone by my presence."

Ricardo Eichmann has said he doesn't want a tear-jerker story written about him: "It is an affront to the six million who died to try and elicit sympathy for me." But his life story is very much a case of the sins of the father being visited on the son. "It's like a rocket. It shoots off into space, but it leaves its fallout behind it and it takes its toll."

I ask him about his personal relationships. What did he tell friends and acquaintances about his father? "I used to just say, 'He died as a consequence of the war.' I suppose they imagined him dying in some act of heroism. But when I met my wife, she already knew who I was. She was a history student specialising in the Third Reich. She knew almost more about Eichmann than I did."

The fallout for Ricardo Eichmann also affected his professional life. He wanted to be a pilot but broke off his training when, during a drill for a chemical warfare attack, the trainee pilots were asked to enter the 'Eichmann soup chambers'. Ricardo Eichmann walked out and began his archaeology degree.

He has chosen a faculty that uses unearthed objects to make sense of the past. "Perhaps if Eichmann had been imprisoned for life we could have used him to understand the mentality of the Nazis more, of how and why they committed the horrors."

But Ricardo Eichmann doesn't want to dwell on the past. He has worked hard on himself. He has agonised over the fact that his father was a Nazi criminal, and has carried on with his life. "I had pushed my father aside. I had dealt with it psychologically, but then you, the journalists, came and brought back my father's ghost and now I have to deal with it again. Perhaps this is my fate."

But even if the journalists had not come, even if the publishers were not pushing for a book that Ricardo Eichmann says he will not write, he would have had to explain the past to his two sons, aged six and eight. He had taught them about prejudice with a book about Sarah, a Jewish girl, and Judith, a non-Jewish girl, and had taught them about the bad men in the brown uniforms. He felt they were too young to deal with any more than that, but two weeks ago a journalist visited their home. Ricardo Eichmann's elder son, Gaspar, asked why the man had come.

"I said, 'He came to ask about our family during the war.' He said, 'What about them?' I was going to fob him off, but I took a deep breath and said, 'He came to ask about Daddy's father.' I said that he was a bad man and he believed in the man with the little brown moustache. He asked if they punished him and I said, 'Yes, he went to prison for two years.' Then he asked, 'And then?' and I said, 'He ended up sort of, on the gallows, like in your Lucky Luke comics'."

For many years Ricardo Eichmann was silent about the past. He had decided that if journalists ever wanted to find out about him, they would just have to observe him, to follow him around, to judge by his actions that the apple had fallen a very long way from the tree. But as requests for interviews began rolling in, he found himself opening up. "I had and have nothing to hide. The journalists are my psychologists. But mainly I am doing this for my children. If I talk about Eichmann, my father, perhaps they will not be asked about Eichmann, their grandfather."

Giles Smith returns next week.