"I am still in Sobibor 67 years on," the trembling man told Court 101. "I still have nightmares about the place. They are so vivid that they are real to me. I can never escape, this is what I have to live with… this is the price I paid for getting out."

Thomas "Toivi" Blatt is one of a handful of survivors from the Nazi extermination camp in occupied Poland, and the man most likely to incriminate John Demjanjuk, an alleged SS guard at Sobibor, in what has been billed as the last Holocaust trial.

Yesterday in a Munich court, Mr Blatt, 82, told judges how he watched his father being brutally clubbed in the face minutes before his parents and 10-year-old brother were dispatched to the gas chambers – among 250,000 Jews who were systematically slaughtered at the camp during World War II.

Both the chief witness and the accused in this trial are in their eighties, yet they could hardly have looked more different. Lying prone and fully dressed in a hospital bed, tucked away in the corner, was the 89-year-old, Ukrainian-born Demjanjuk.

He has refused to say anything during the trial, which opened in December, but his appearance in court yesterday bordered on farcical. At times, he appeared to be asleep, a bluish baseball cap pulled over his eyes. He was a figure, almost forgotten. Instead, all eyes were on the sprightly, yet clearly emotional, octogenarian on the witness stand, who recounted his personal tale of horror in a heavily accented mixture of English and German over the course of five hours of testimony.

Mr Blatt only survived Sobibor because he was selected as a so-called "work-Jew". Instead of being murdered upon arrival, he was chosen to shave the heads of women in a barrack room before they were dispatched to the gas chambers next door. The women's hair would ultimately be sent to Germany and turned into blankets for U-Boat crews.

His evidence is expected to play a vital role in determining the outcome of the trial, even though he is not able to positively identify Demjanjuk as being at the camp. "I can't say I remember Demjanjuk's face, but frankly I can't even recall that of my father or my mother after so many decades," he told the court. However, German prosecutors say they will present evidence from Russian World War II files which will prove conclusively that Demjanjuk was working as an SS guard in Sobibor at the time of the atrocities described by Mr Blatt, and is therefore complicit in the murder of the 27,900 Dutch Jews.

Mr Blatt was rounded up by the SS in 1943 in the Jewish ghetto village of Izbica, 43 miles from Sobibor. He recalled yesterday that although the camp was renowned as a death factory, he was shocked on arrival to see that it was almost beautiful.

"There was a little railway station. The camp commandant's house was called the 'Swallow's Nest' and the barbed wire fences had been interwoven with green twigs," he said. "I was shocked but in the back of my mind I knew I was going to die."

Mr Blatt described how he was put in a group of 200 Jews who were driven to the camp in lorries. When they disembarked, they were surrounded by dozens of Ukrainian guards wearing black SS uniforms and brandishing whips and rifles.

The court was then thrown into darkness as a map of the camp was projected on to the wall and, with a juddering hand, Mr Blatt traced his route with a ballpoint pen.

"There were shouts of Raus! Raus! (Out! Out!). One of the German officers asked if there were any tradesmen in our group. My father said he was a tanner. The camp didn't need any tanners so the officer just hit him in the face with a club," Mr Blatt told the court. He never saw his parents and brother again.

His fate, however, led not to the gas chamber. He was selected to work for the Nazis. "I was only 15 but strong and healthy. I just pleaded 'Take me! Take me!' to the officer and suddenly he said to me, 'Come on, little one'," Mr Blatt continued.

From then until his miraculous escape five months later, he was forced to witness the horrific day-to-day workings of the Nazi death machine. He was allowed to live, albeit under the constant threat of death at any time. His memories of working at the camp's "barber shop" were chilling.

"The Dutch Jews were all gullible. They had been told that they were being given a shower for sanitary reasons and had to have their hair cut. One Dutch woman even asked me not to cut her hair too short; she still believed she was not going to die," he recounted. "But the Polish Jews knew exactly what faced them. One Polish woman asked me why I was helping the SS. 'How can you do this?' she asked. I told her I was trying to survive."

Mr Blatt recalled in chilling detail how Sobibor's 120 Ukrainian SS guards used to herd Jewish men, women and children up the "Road to Heaven" with whips and bayonets towards the gas chambers. Once there, the Jews were killed by carbon monoxide exhaust fumes in a process that could take as long as 40 minutes.

"When the guards came back they had blood on their boots," he said. "They used the bayonets to cram the people into the gas chambers." The frail and elderly who could not walk were taken to a nearby chapel and routinely shot in the back of the head. Later a railway was specially built to carry them to the gas chambers. The Polish Jews murdered in Sobibor hoped to the very last that they might find a way of getting out. On the mornings after the mass gassings, Mr Blatt was ordered to sweep the "Road to Heaven" with a broom.

"I used to pick up hundreds of bits of coloured paper lying in the road. It was the money which people had kept clenched in their fists after being stripped naked," he told the court. "They hoped until the last that they would be able to buy their freedom. When they finally realised it was hopeless, they tore up the money. They were defiant to the end, they did not want the guards to get it."

Describing the Ukrainian guard unit in Sobibor to which Demjanjuk is alleged to have belonged, Mr Blatt said they used to round up prisoners and shoot them at random.

One of his jobs was to search through the clothing of the Jews after they had been gassed, looking for valuables and money. "The Ukrainians wanted us to provide them with gold and money to buy vodka and prostitutes," he said.

"We were terrified of them, they were far worse than the Germans… they were the most important personnel in Sobibor," he added. "Without them, the death factory wouldn't have functioned."

The trial continues. A verdict is expected in April.

Death camp break-out: How Sobibor Jews fought back

Thomas "Toivi" Blatt, a Sobibor survivor who gave evidence yesterday, participated in one of the very few attempts by Jewish prisoners to escape from the death camps. When he was assigned work duty at the camp it was said that the only way out of it was "with the smoke, travelling with the wind". But thanks to the leadership of a charismatic Soviet prisoner called Sasha Pechersky, Blatt and the other prisoners planned and executed a mass escape in October 1943. Most of them died in the attempt, killed by mines or the bullets of the surviving Nazi guards, but around 50 survived.

"We knew our fate," wrote another survivor, Yitzhak Arad. "We knew that we were in an extermination camp and death was our destiny. We knew that even a sudden end to the war might spare the inmates of the 'normal' concentration camps, but never us. Only desperate actions could shorten our suffering and maybe afford us a chance of escape. And the will to resist had grown and ripened. We had no dreams of liberation: we hoped merely to destroy the camp and to die from bullets rather than from gas. We would not make it easy for the Germans."

On the appointed day the leaders of the uprising killed the camp's acting commander, another SS officer and two Ukrainian guards.

"Sasha was surprised at how well the plan had gone so far," wrote another survivor, Richard Rashke, "[but] he realised there could not be an orderly march through the front gate. He stood up and addressed the assembled prisoners… 'Our day has come,' he said. 'Most of the Germans are dead. Let's die with honour. Remember, if anyone survives, he must tell the world what has happened here.'"

Blatt later wrote: "The remaining Germans and some guards with machine guns now blocked the main gate. People were killed and the frontline Jews, mostly unarmed, fell back, then a new wave of determined fighters pushed forwards again in a suicidal thrust. Someone was trying to cut an opening in the fence with a shovel.

"Within minutes, more Jews arrived. Not waiting in line to go through the opening under the hail of fire, they climbed the fence. Though we had planned to touch the mines off with bricks and wood, we did not do it. We couldn't wait; we preferred sudden death to a moment more in that hell.

"Corpses were everywhere. The noise of rifles, exploding mines, grenades and the chatter of machine guns assaulted the ears. The Nazis shot from a distance while in our hands were only primitive knives and hatchets.

"We ran through the exploded minefield holes, jumped over a single wire marking the end of the minefields and we were outside the camp. Now to make it to the woods ahead of us. It was so close. I fell several times, each time thinking I was hit. And each time I got up and ran further, [reaching] the forest at last. Behind us, blood and ashes. In the greyness of the approaching evening, the towers' machine guns shot their last victims."

Sobibor Extermination Camp