The crematorium contains a large hall, a gas chamber and a furnace. People are assembled in the hall, which holds 2,000. They have to undress and are given a piece of soap and a towel as if they were going to the baths. Then they are crowded into the gas chamber which is hermetically sealed. Several SS men in gas masks then pour into the gas chamber through three openings in the ceiling a preparation of the poison gas maga-cyclon. At the end of three minutes all the persons are dead. The dead bodies are then taken away in carts to the furnace to be burnt.

We marched into the commercial heart of Auschwitz, warehouses of the body-snachers where hundreds of prisoners worked frantically to sort, segregate and classify the clothes and the food and the valuables of those whose bodies were still burning, whose ashes would soon be used as a fertilizer.

It was an incredible sight, an enormous rectangular yard with a watchtower at each corner and surrounded by barbed wire. There were several huge storerooms and a block of what seemed like offices with a square, open balcony at one corner. Yet what first struck me was a mountain of trunks, cases, rucksacks, kitbags and parcels stacked in the middle of the yard.

Nearby was another mountain, of blankets this time, fifty thousand of them, maybe one hundred thousand. I was so staggered by the sight of these twin peaks of personal possessions that I never thought at that moment where their owners might be. In fact I did not have much time to think, for every step brought some new shock.

Heinrich Himmler visited Auschwitz camp again in January 1943. This time I was glad to see him arrive, though not because I still nursed any faint hope that he would improve our lot through benevolence or any sense of justice. His presence was welcome to us all merely because it meant that for one day there would be no unscheduled beatings or killings.

He was to watch the world's first conveyor-belt killing, the inauguration of Commandant Hoess's brand new toy, his crematorium. It was truly a splendid affair, 100 yards long and 50 yards wide, containing 15 ovens which could burn three bodies each simultaneously in 20 minutes, a monument in concrete, indeed, to its builder, Herr Walter Dejaco.

Himmler certainly saw an impressive demonstration, marred only by a timetable that would have caused concern in many a small German railway station. Commandant Hoess, anxious to display his new toy at its most efficient, had arranged for a special transport of 3,000 Polish Jews to be present for slaughter in the modern, German way.

Himmler arrived at eight o'clock that morning and the show was to start an hour later. By 8.45, the new gas chambers, with their clever dummy showers and their notices - "Keep Clean", "Keep Quiet" and so on - were packed to capacity. The SS guards, indeed, had made sure that not an inch of space would be wasted by firing a few shots at the entrance. An SS man, wearing a heavy service gas mask, stood on the roof of the chamber, waiting to drop in the Zyklon B pellets, which released a hydrogen cyanide gas. His was a post of honour that day, for seldom would he have had such a distinguished audience, and he probably felt as tense as the starter of the Derby. By 8.55, the tension was almost unbearable. The man in the gas mask was fidgeting with his boxes of pellets. Somewhere a phone rang. Every head turned towards it. A junior NCO clattered over to the officer in charge of the operation, saluted hastily, and panted out a message. The officer's face stiffened, but he said not a word. The message was: "The Reichsführer has not finished his breakfast yet." At last, however, everything was ready for action. A sharp command was given to the SS man on the roof. He opened a circular lid and dropped the pellets quickly on to the heads below him. He knew, everyone knew, that the heat of those packed bodies would cause these pellets to release their gases in a few minutes; and so he closed the lid quickly. The gassing had begun. Having waited for a while so that the poison would have circulated properly, Hoess courteously invited his guest to have another peep through the observation window. For some minutes Himmler peered into the death chamber, obviously impressed, and then turned with new interest to his commandant with a fresh batch of questions. Special lifts took the bodies to the crematorium, but the burning did not follow immediately. Gold teeth had to be removed. Hair, which was used to make the warheads of torpedoes watertight, had to be cut from the heads of the women. The bodies of wealthy Jews, noted early for their potential, had to be set aside for dissection in case any of them had been cunning enough to conceal jewellery - diamonds, perhaps - about their person.

Himmler waited until the smoke began to thicken over the chimneys and glanced at his watch. It was one o'clock. Lunchtime, in fact. He shook hands with the senior officers, returned the salutes of the lower ranks casually and cheerfully, and climbed back into the car with Hoess. Auschwitz was in business.

Early in March 1942, in rebellion against the deportation laws, Vrba ripped the yellow Star of David off his clothes and left his Czechoslovakian home in a taxi, heading for Britain via Hungary. Later, having been intercepted by frontier guards, he was first sent to the Novaky transition camp in Slovakia, where he tried to escape, but again was caught and beaten. On June 14 1942 he was deported to the Majdanek concentration camp in Poland and two weeks later, on June 30, to Auschwitz. After six months in Auschwitz, he was transferred to Birkenau (Auschwitz II) and had the number 44070 tattooed on his arm.

From August 1942 until June 1943 Vrba was assigned - both in Auschwitz and in Birkenau - to work in the special slave labour unit that handled the property of those who had been gassed. In camp slang, the unit was known as "Canada" because of the food and the gold and other precious materials that the Germans confiscated from the luggage of the incoming "resettlement" deportees. The Auschwitz treasures from "Canada" were packaged for Germany, and the gold was quickly melted into ingots and deposited in the Reichsbank.

A major aspect of Vrba's duties during 1942 and 1943 was to be present at the arrival of most transports of deportees and to sort the belongings of the gassed victims. From this vantage point he was able to assess how little the deportees knew about Auschwitz when they entered the camp. Their luggage contained clothing for all seasons and basic utensils, a clear sign of their naive preparation for a new life in the area of "resettlement" in the east.

In the summer of 1943, Vrba improved his position for collecting information when he was appointed registrar in the quarantine camp for men. At the beginning of 1944, he noticed that preparations were under way for an additional railway line, for an expected transports of Jews who, in the SS camp language were called "Hungarian salami". Transports from different countries, Vrba would later explain, were characterised by certain long lasting provisions packed in the prisoners' luggage for the final journey into the unknown.

As he subsequently wrote: "When a series of transports of Jews from the Netherlands arrived, cheeses enriched the wartime rations. It was sardines when a series of transports of French Jews arrived, halva and olives when transports of Jews from Greece reached the camp, and now the SS were talking of 'Hungarian salami', a well-known Hungarian provision suitable for taking along on a long journey."

For almost two years he had thought of escape, at first selfishly, because he had merely wanted his freedom, but now, "I had an imperative reason. It was no longer a question of reporting a crime but of preventing one." He began his first scientific study: to assess every unsuccessful escape attempt, to analyse its flaws and to correct them.

On Friday, April 7 1944, (the eve of Passover), Vrba and Wetzler sneaked into a previously used hideout sprinkled with gasoline-soaked tobacco to prevent the dogs from sniffing them out. They stayed there for three nights, until the camp authorities assumed that the two men had already got beyond the outer perimeter. When the cordon of SS guards that had surrounded that perimeter was withdrawn, Vrba and Wetzler were ready to sneak out.

They knew one thing for certain: as shaven-headed inmates, clad in striped pyjamas and with numbers tattooed on their arms, there was no point in relying on any help in the world outside Auschwitz. "At the moment of our escape," explained Vrba, "all connections with whatever friends and social contacts we had in Auschwitz were severed, and we had absolutely no connection waiting for us outside the death camp where we had spent the past two years." As he later phrased it: "We were de facto written off by the world from the moment we were loaded into a deportation train in the spring of 1942. To start with, we had to step into a complete 'social vacuum' outside Auschwitz. The only administrative evidence of our existence was an international warrant about us, issued telegraphically and distributed to all stations of the Gestapo."

The Vrba-Wetzler report continues to generate historical debate to this day. Many, including Vrba himself, have questioned whether the report was disseminated and acted upon as rapidly and as forcefully as it should have been. In an unanswerable "what if", Vrba continued to question to his last day whether more victims could have been saved had the allied and the Jewish leadership of the time pursued a more vigorous course of action in light of his report. This line of thought has at times made his ideas somewhat incongruent with the predominant Israeli historical narrative concerning the events of that time. Whereas the two escapees accurately predicted the fate of the Hungarian Jews, what they could not have foreseen was that their postwar memoirs and documented report would be kept from the Israeli Hebrew-reading public.