It was when the guards began burning piles of bodies in the open because the crematorium could not keep up with the task that Marek Dunin-Wąsowicz realised he was being held in a camp whose purpose was not just to “concentrate”, but systematically to murder thousands of people.

In the autumn of 1944, the 17-year-old Pole saw trainloads of Jews, most of them from Hungary, being taken straight to the gas chambers at Stutthof. Others were gassed inside an adapted railway carriage, set on tracks to trick prisoners into believing that they were being transported to another destination.

But the point where certain knowledge of the Nazis’ plans for mass murder could have shaken inmates into action had already passed. “The one thing the Nazis succeeded in at in the camp was that they pushed us inmates to a point where we became indifferent to the horror around us,” Dunin-Wąsowicz told the Guardian.

“When your friends were being beaten up around you, your first thought was, at least they didn’t get me. When they carried out public executions at lunchtime, you were distraught not because people were dying, but because you were missing out on food. We existed at a level where our empathy had been beaten out of us.”

On Monday, 74 years after escaping near-certain death, Dunin-Wąsowicz will for the first time face one of the men who stopped him and the thousands of others from escaping from the concentration camp east of what is now the city of Gdansk, in Poland.

He will be the first witness to give testimony in what is likely to be one of the last trials against an individual charged over the Holocaust. A former camp guard and member of the SS Totenkopfsturmbann (Death’s Head Battalion), Bruno Dey, has been charged by a court in Hamburg with accessory to the murder of 5,230 people. Both the accused and the co-plaintiff are 93.

Facebook Twitter Pinterest A gas chamber at the Stutthof concentration camp. Photograph: Getty Images

Dunin-Wąsowicz arrived in Stutthof in May 1944, following the arrest of his entire family for involvement in the Polish resistance effort against the German occupation. As a member of Szare Szeregi (Grey Ranks), a paramilitary scouting organisation, and then the Polish Home Army, he had carried out minor acts of sabotage, vandalising Nazi posters and reporting on the movement of the Wehrmacht.

He faced squalid living conditions in the camp: around 5,000 of the victims listed on Dey’s charge sheet died of a typhus epidemic after being denied food, water and medication. Toothaches, Dunin-Wąsowicz recalled, were generally treated by pulling out the infected teeth. Anaesthetic was unavailable; patients were simply knocked unconscious ahead of operations.

He survived the camp partly thanks to a Polish doctor who advised him to drop a log on to his foot so he could get a break from gruelling forced labour shifts in the sick bay. At regular intervals, the same doctor would smash up his toe again so the young prisoner couldn’t be drafted back to work in the field.

Later, he and his brother managed to get vaccinated because they had been assigned administrative tasks that made them indispensable to the organisers of the concentration camp.

In January 1945, with the Soviet army advancing, the two brothers were made to join one of the death marches in the direction of the town of Lębork. Snow was deep and temperatures were freezing. Those who could walk no further were shot on the spot, creating a vicious cycle where those at the back of the march exhausted themselves further by racing not to be the last in line.

In what he described as a “miracle”, the Dunin-Wąsowicz brothers managed to escape into the woods one night. Thousands of others on the march were later executed or drowned in the freezing Baltic sea.

For the first few decades after the end of the war, Dunin-Wąsowicz tried to suppress the memories of his time in the camp. Around ten years ago, something changed: he felt he wanted younger people to know exactly what had happened in the camps, he said.

Facebook Twitter Pinterest Bruno Dey, 93, in court in Hamburg. He is accused of aiding and abetting the murder of 5,230 people. About 25 camp survivors appear as joint plaintiffs. Photograph: Daniel Bockwoldt/AP

When Germany’s Central Office for the Investigation of National Socialist Crimes identified Dey as one of the few surviving guards at the Stutthof camp, Dunin-Wąsowicz did not hesitate to join the prosecution as one of about 20 co-plaintiffs.

During the trial, Dey has admitted seeing people being led into the gas chamber, and hearing screaming and banging sounds behind the locked door. But he has denied being guilty of accessory to murder, and complained that the trial had “destroyed” the last years of his life.

In Dunin-Wąsowicz’s recollection, SS guards like Dey carried out three types of tasks: overlooking the camp from watchtowers, armed with machine guns; watching over prisoners while they worked outside the compound; and escorting them to places where they were executed.

Even if brutal beatings were usually administered by the kapos – mostly German prisoners tasked with supervising other inmates – he said the SS guards played a crucial role: “The kapos beat prisoners to death because they were being supervised. Their viciousness was an expression of their will to survival – they had to excel at their task to avoid being made ordinary prisoners again.”

His aim in joining the prosecution, he said, was not to “seek revenge”: “I don’t necessarily want him to go to prison. But ultimately one has to pay for one’s mistakes. It’s a question of justice.”

What matters to him now is that the European public remembers what took place in the camps, and remembers that the prisoners included nationals from more than 20 European nations. He said: “It would give me closure if this trial helps the next generation of Germans, of Poles, of all Europeans, to learn a lesson when it comes to the revival of fascism, racism and xenophobia.”