The Friend Who Cooked Dinner: A Stasi Murder Plot on the Sinai, 1981

He was seventeen. He said on camera, years later: "We were, quite literally, prisoners."

He has described what was done to him inside in a memoir and on camera. He spent eight days in a cellar cell in his underwear, with frost on the walls, a rubber seal around a door without a spyhole, and a caged light that never went out. One February night he was blindfolded, led into a courtyard and read a death sentence, and he heard the order to fire. Nobody fired. He said: "Inside I was as good as dead. It took years before I could even talk about it."

The informer was Peter Haack. He was born in 1942, and he had drifted. He volunteered for three years in the West German army and felt at home there. After that he drove for a building firm in Munich, then for the American army, and married an Austrian woman, mainly so that she could stay in Germany. By 1969 he was living in Kreuzberg, in West Berlin, and working on a building site on the other side of the Wall, in East Berlin, on a visa renewed every three months.

In August 1976, by his account, his wife flew to Sofia with papers for a refugee sewn into the lining of a vanity case, and their daughter, then two, along to make it look like a holiday. She was arrested at the airport. She was released against a large sum of money, and the Bulgarian route was finished.

That summer he turned up in Platania and did not manage to get close to the family. In the summer of 1979 he was sent back.

They became friends. Haack spent that holiday with the family, and the next summer's too, and came to visit them at home. He worked his way into their trust until they thought of him as the family's best friend. After that first summer, the Stasi's orders to Haack were to invite the family to London, or to go and see them at home.

At a clinic in Frankfurt he was treated for plastic splinters in his face and legs, for smoke poisoning and for shock, and he went home the next day. The police, he says, told him it had probably been a cable fire, an electrical short circuit.

In East Germany, Haack's partner was expecting their child. His daughter was born on the second of June 1981, seven weeks before the meal on the beach. That month, from London, he telephoned the Welsches. He had a photo job in Israel in July, he said, and a car, and they could come along.

In early July Haack flew from London to Tel Aviv and took a room at a hotel in Acre, on the coast north of Haifa. At the hotel he met a young woman of about twenty-five who said she was an American Jew. When he told her about the tour he was planning with a German family, she wanted to come, and he invited her. Welsch's book calls her Susan.

Welsch took it to his doctor, who looked at the writing and confirmed his fear: Peter had thallium poisoning too. With a certificate saying Peter's life was in danger, Welsch went to Deutsche Welle, West Germany's overseas radio service, in Cologne. That evening an emergency message went out on the service to South America. It asked Mr Peter Haack from London, now travelling in Argentina, to call Mr Wolfgang Welsch in Germany at once, because he had a life-threatening poisoning.

Welsch wrote: "Peter Haack had never been to Argentina. And yet this was where he had died." He was sure now that Haack was in East Berlin. As long as East Germany stood, he would stay there.

He took the story to the press. In 1990, he says, the head of the Berlin office of one of West Germany's big news magazines heard him out, looked at his evidence, and told him: "This suspicion has no substance. The Stasi gave no orders to kill. That simply did not exist." The telephone calls started soon after. By his account they went on for weeks, anonymous voices telling him his last hour would strike soon. Shortly before Christmas 1991 one caller spelled it out: "If you don't stop your slanderous accusations, we will finish what we haven't managed so far. And this time we'll get you." In 1992 he left Germany for Costa Rica.

The Stern, the big Hamburg weekly, took him seriously. Its reporters, he says, spent a whole night questioning him in a Hamburg hotel. Their own account of the investigation says: "The reporters are sceptical. But the first checks show that Welsch is no crank." Working with a Berlin police unit set up to investigate the crimes of the East German state, they followed Haack's trail through Britain, Greece and Israel for eight months.

Haack confessed. He told the court he had mixed the thallium into the meatballs as agreed, and that the plan had come from the top of the Stasi. He named Fiedler, and described the meetings and the poison. He said he had signed up with the Stasi in 1970 to keep seeing a girlfriend in East Berlin, and because the work seemed interesting and adventurous. He had liked the Welsch family very much, he said, and the idea of killing them had been rather unpleasant to him. But he had feared that if he refused he would lose his place as a good informer, and might never see his own family again. On the dose, his story kept changing. First it had been a knife-tip, meant only to make Welsch ill. Then it was a third of what was left, and then a half. A toxicologist from the Bavarian criminal police held up a glass vial with one gram of thallium sulphate in it, about the median lethal dose, and Haack said he had used that much. He said: "No less, but no more."

In the same interview he said the young woman had been a full-time Stasi officer, and that she was still being sought, because murder does not expire. Nobody has ever found out who she was.