The first experimental gassing took place in September 1941, when Lagerführer Karl Fritzsch, at the instruction of Rudolf Höss, killed a group of Soviet prisoners of war by throwing Zyklon B crystals into their basement cell in block 11 of Auschwitz I. A second group of 600 Soviet prisoners of war and around 250 sick Polish prisoners was gassed on 3–5 September.[29] The morgue was later converted to a gas chamber able to hold at least 700–800 people.[30] Zyklon B was dropped into the room through slits in the ceiling.[28] In the view of Filip Müller, one of the Sonderkommando who worked in crematorium I, tens of thousands of Jews were killed there from France, Holland, Slovakia, Upper Silesia, Yugoslavia, and from the Theresienstadt, Ciechanow, and Grodno ghettos.[31] The last inmates to be gassed in Auschwitz I, in December 1942, were 300–400 members of the Auschwitz II Sonderkommando, who had been forced to dig up that camp's mass graves, thought to hold 100,000 corpses, and burn the remains.[32]
These people had a blue stamp in their registration cards, meaning that they were exempt from deportation. They were Jews who had British or American citizenship. The Nazis saw these Jews as ‘exchange Jews’, and they would attempt to exchange each one of them for five to 10 Germans; especially military prisoners of war. In fact, few exchanges ever occurred.
Our trip, full of suspense, took us past the baroque palace of Oranienburg, built at the time of Frederick the Great, through the sand of Brandenburg and through deserted pine forests, thence to a large settlement. Suddenly we saw in front of us high walls (about fourteen feet) which, at intervals of two hundred yards, were crowned by watchtowers, so that the whole camp gave the impression of a Chinese city as we knew it from pictures. We drove through an iron gate, and soon after through a second gate in a second inner wall about a hundred feet from the first one. In the space between the two walls there were barracks with administration and treasury buildings, and vegetable and other gardens. The inner gate, which led through the main watchtower, bore the inscription 'Work Makes Free'—an inscription which many inmates of the camp, after years of work and vain hope for release, will probably take as sarcasm.

“There is, of course, all possible types of administration done by the Germans of the time,” Thijs Baynes, the filmmaker behind the project, told the Guardian. “And there is an even bigger circle of circumstantial evidence. What [Dutch Nazi party] members were in the neighborhood? What connections were with the Gestapo? Where were Gestapo agents living?

Probably my earliest memories of anything at all are of walking through the streets of Trenčín and people stopping in their tracks and saying with amazement: “You’re back!” “What a miracle that you’re alive!” I understood as a three-and-a-half to four-year-old that I was a miracle because I got to hear it so many times, but I didn’t really understand what the word meant. Only much later could I recognise what a miracle it really was that I had survived, when I learned that of the thousands of Slovak men and women who were deported to Auschwitz, only a few hundred returned.
Between 1933 and the fall of Nazi Germany in 1945, more than 3.5 million Germans were forced to spend time in concentration camps and prisons for political reasons,[18][19][20] and approximately 77,000 Germans were executed for one or another form of resistance by Special Courts, courts-martial, and the civil justice system. Many of these Germans had served in government, the military, or in civil positions, which enabled them to engage in subversion and conspiracy against the Nazis.[11]