Arguments based on the physical structure of the chambers (ventilation, construction and other concerns) spring from the postwar examination of the camps. However, there is ample evidence that Nazis fully or partially destroyed many execution facilities to conceal evidence of their crimes.<ref>http://www.ushmm.org/wlc/en/article.php?ModuleId=10005189</ref><ref>http://remember.org/History.root.rev.html</ref>
A letter from Karl Bischoff, the head architect at Auschwitz, to the German Armament Works dated March 31, 1943 orders “three gas tight doors” for Crema 3 following “exactly the size and construction of those already delivered” for Crema 2. Bischoff reminded the manufacturer that the doors had to have a spy-hole of double 8-mm glass “with a rubber seal and metal fitting.” The order was characterized as “very urgent.”
There are also many photographs of actual gas-tight doors that were found all over Auschwitz immediately after the war. One, which had been used in either Crema 4 or 5, had a peep-hole covered with a heavy mesh screen and still had a gas-tight seal still around the edge, just as Bischoff’s letter requested. The blueprints for Crema 2 show ventilation ducts in the walls (labeled ‘Entlüftung’) and the remains of the ducts can still be seen in the ruins. In the archives there is also a request for a “handle for the gastight door” and a request for “twenty-four-gastight anchoring screws for gas tight doors” for Cremas 4 and 5.
The walls and ceilings of the gas chambers were plastered and whitewashed as numerous eyewitnesses have testified. By the time Leuchter arrived at the camp to take his samples, the plaster was gone and the exposed brick had been exposed to 40 years of rain, sun and snow. As HCN leaves only a thin blue chemical residue on surfaces, any “Prussian Blue” residue from the HCN would have collected on the surface of the plaster and would not have left a substantial presence on the bricks and mortar or concrete underneath.
Leuchter collected 31 handful-sized samples of bricks and mortar from the cremas and one control sample from the delousing chamber in Birkenau. By the time he crawled into the ruins of Crema 2, the plaster was long gone and only the bricks and mortar and concrete remained. Cremas 4 and 5 were constructed entirely of brick. They were totally destroyed before the end of the war. Only the concrete foundations remain and bricks have been gathered from around the area and loosely stacked up to show the general outline of the floor plan of the buildings. The bricks that Leuchter sampled did not necessarily come from anywhere near the gas chamber rooms.
In the laboratory the individual samples were ground up into powder. Any trace of the HCN residue that might have been there became a miniscule part of the entire sample. A more appropriate method would have tested only the surfaces of the sample. Testing the total amount of the ground up powder was like trying to analyze the color and chemical structure of paint on the inside of a wall by looking for it in the boards and masonry behind the drywall. In the case of Cremas 4 and 5, it would like analyzing the materials from another room entirely.”
The fact that even “insignificant traces” were found in the ruins of the gas chambers after all these years of being exposed to the elements is proof that there WERE gas chambers in Auschwitz-Birkenau.</ref>http://www.hdot.org/en/learning/myth-fact/leuchter</ref>
A properly authorized and meticulously conducted, rigorously scientific study done by Polish authorities in 1994 found that “''in spite of the passage of a considerable period of time (over 45 years) in the walls of the facilities which once were in contact with hydrogen cyanide the vestigial amounts of the combinations of this constituent of Zyklon B had been preserved. This is also true of the ruins of the former gas chambers''.”
== Holocaust Denial in Germany ==