I didn't want to open another thread about this, since there are quite a few already, so I'm posting into this one, which I think is the most fitting.
Let's start with a testimony by a survivor, Henryk Tauber:
The roof of the gas chamber was supported by concrete pillars running down the middle of its length. On either side of these pillars there were four others, two on each side.
"
Two on each side." That is, two on the western and two on the eastern side. Let's see what Pressac has to say about that:
According to the American aerial photograph of 24th [25th?] August 1944, the four introduction points were located along a line running the length of the room in the eastern half. In the present ruins, two of these openings are still visible at the southern end but in the western half. Nobody up to now seems to have been concerned by this contradiction, nor to have explained it.
"
According to the American aerial photograph [...] the four introduction points were located along a line running the length of the room in the eastern half." The aerial photographs and Henryk Tauber's testimony contradict each other. Not to mention two of the supposed holes (which are completely benign, as we shall see later) are today visible at the western end of the roof slab, but are located on the eastern end on the aerial photographs.
Next, Charles D. Provan:
No matter what one thinks of the authenticity of the smudgey marks, it is impossible to view them, whether authentic or not, as 'vents.' [...] [air photos] cannot be used to prove or disprove that the underground rooms were gassing facilities. [...] So we are hesitant to use the aerial photographs as proof that there were roof vents for Zyklon B.
[...]
if [these smudges] are shadows [cast by the low chimneys], the height has been calculated as about 3 meters, using the known height of the Krematorium chimney, and the length of its shadow as a reference.
[...]
some of the photographs of Auschwitz-Birkenau show roof marks where no Zyklon B vents are supposed to be.
If they are shadows, then they are obviously too long. Their angles are wrong, too:

Next, Daniel Keren, Jamie McCarthy, and Harry W. Mazal with their "holes report":
It is impossible to observe the Zyklon holes themselves in any of the aerial photographs.
[...] they are too large, and not in the correct shape, to represent the actual holes.
Pretty clear, I'd say. But then they go on:
The smudges are too large to belong just to the holes themselves. They probably correspond to the tamping down of a trail on the roof by the SS men detailed to introduce the canisters [...] moving from vent to vent.
But the earth appears white in every single aerial photograph, except for areas with vegetation. The only possibility that the smudges are trampled earth is if the Germans dipped their boots into black tar before they climbed on the roof. Further to this, the claim that the smudges are "
a path of compacted earth produced by personnel" is absurd when one takes crematorium III into consideration, where the smudges are in odd angles for some 3 meters. It would mean the Germans walked from vent to vent in these odd angles whereby they would jump from one vent to another some 3-4 meters away! Who ever said that "white men can't jump" is clearly mistaken!
They admitted it is impossible to observe any holes in the smudges, but then they claim they have:
identified four small objects within the smudges, all slightly elevated above the level of the roof. [...] [which are] very difficult or impossible to detect in separate images [...] In all probability, these correspond to the four 'chimneys' above the holes in the roof, as clearly visible in the Train Photograph.
First, let's mention that the expert who did the analysis is Carroll Lucas, a retired CIA photo expert who the authors claim has: "
more than fifty years experience in aerial and satellite photo analysis." Carroll Lucas served in the US Army Air Force between 1943 and 1946, and if he was at least 18 at the time, it would make him 79 or 80 years old when he analysed the photographs. Mr. Lucas apparently has very good eyesight, even at his age.
Secondly, the objects in the train photograph do
not correspond with the aerial photographs, as proven in the Irving trial below:
Robert Jan van Pelt: Today, these four small holes that connected the wire-mesh columns and the chimneys cannot be observed in the ruined remains of the concrete slab.
[...]
It is very difficult to determine the size of the objects, because of the way the shadow works.
[...]
David Irving: What have you to say about the spacing of those smudges when you compare them with what I call the tar barrels on the roof in the other photograph? They are differently spaced, are they not? [...] Would it not be correct to say that in fact there is a very uneven spacing in the four tar barrels visible from the ground, whereas the smudges on the roof appear to be admittedly irregularly spaced but in a totally different way. Therefore, they have no connection whatsoever with the protuberances that are visible from ground level.
Robert Jan van Pelt: I have no comment on that.
[...]
David Irving: You have not seen any holes in the roof, have you, in the -- when you went there? You have not found any holes?
Robert Jan van Pelt: I have not seen the holes for the columns, no.
David Irving: Not for the introduction of the cyanide?
Robert Jan van Pelt: No.
Professor van Pelt believes the smudges to be chimneys (through which Zyklon-B was introduced) and their shadows. When David Irving confronts him with the fact that these smudges or "chimneys" are in different locations than the February 1943 "train" photograph:

van Pelt responds with "
I have no comment on that." The objects on the February photograph are, as Irving states, barrels:


The lines in the drawing below represent the possible locations upon which the objects on the roof (and holes) were positioned. At none of these locations are there any holes or traces of refilled holes found in the remains today, except for one which was made by the Soviets or Poles, but it's on the wrong (western) side of the roof, whereas the objects are on the eastern side. The hole is also shifted around 3 meters to the south of the first object. This proves the objects on the roof were not introduction chimneys:

At first glance there appear to be five objects on the roof, but the easternmost object is in fact under the window and not on the roof. The westernmost object is barely visible behind the train's smokestack, but can also be seen in the January 1943 photograph:

where it is box-like. What this is, is a mystery, but it was without a doubt construction-related, i.e. building material. The first object to the right of the train's smokestack seems to fit right in with the two barrels next to it on the right, but is in fact quite different upon thorough examination. In fact, the "believers"
always ignore this object, because they have no idea what it is or what it's doing there! Germar Rudolf calculated the size of the object as 75 centimetres here:

This object is not a part of their "four chimneys," instead they claim the third chimney is hidden entirely behind the train's smokestack and can't be seen. They are absolutely positive that this object is
not a chimney, but the other three and one imaginary behind the smokestack are! We can safely assume it was, again, something construction-related.
Kenneth Roy Wilson, an expert in photogrammetry and aerial triangulation, testified in the second Zündel trial in 1988 that in the May 31st, 1944 air photo: "
the patches on top of the morgue at crematorium II were flat and had no elevation." Wilson could not say what the patches were but believed they were
discolorations on the surface of the roof.
For the August 25th, 1944 photo, he likewise testified that: "
the patches were not shadows but did not have any elevation." He could not identify what the patches were or what caused them.
For the September 13th, 1944 photo, he could only detect a slight patch close to the crematorium, but not the other patches. Again he claimed the patches are neither shadows nor have any elevation, but were just discolorations on the surface of the roof. Wilson also believed there was no smoke or haze (due to bombing) present that reduced the quality of the photograph.
So, we've heard what the survivors, historians and the experts have to say, now let's hear what the builders of the "gas chambers" have to say! First, Walter Schreiber (not to be confused with Walther Schreiber, who was the mayor of Berlin from 1953 to 1955, or Walter Paul Emil Schreiber who was a military officer in the Wehrmacht and died in 1952), who was a: "
supervising engineer, I inspected the Huta Corporation and dealt with the Zentralbauleitung of the SS." He gave an interview in 1998, a year before he passed away at the age of 91:
Question: In which positions were you active?
Answer: As supervising engineer, I inspected the Huta Corporation and dealt with the Zentralbauleitung of the SS. I also audited the invoices of our firm.
Question: Did you enter the camp? How did that happen?
Answer: Yes. One could walk everywhere without hindrance on the streets of the camp and was only stopped by the guards upon entering and leaving the camp.
Question: Did you see or hear anything about killings or mistreatment of inmates?
Answer: No. But lines of inmates in a relatively poor general condition could be seen on the streets of the camp.
Question: What did the Corporation build?
Answer: Among other things, crematoria II and III with the large morgues.
Question: The prevalent opinion is that these large morgues were gas chambers for mass killings.
Answer: Nothing of the sort could be deduced from the plans made available to us. The detailed plans and provisional invoices drawn up by us refer to these rooms as ordinary cellars.
Question: Do you know anything about introduction hatches in the reinforced concrete ceilings?
Answer: No, nothing more from memory. But since these cellars were also intended to serve the auxiliary purpose of air raid shelters, introduction holes would have been counter-productive. I would certainly have expressed an objection to such an arrangement.
Question: Why were such large cellars built, when the water table in Birkenau was so extremely high?
Answer: I don't know. Originally, however, above-ground morgues were to be built. The construction of the cellars caused great problems in retention and sealing.
Question: Would it be conceivable that you were deceived and that the SS nevertheless had gas chambers to be built by your firm without your knowledge?
Answer: Anyone who knows anything about what happens on a building site knows that that is impossible.
Question: Do you know any gas chambers?
Answer: Naturally. Everyone in the east knew about disinfection chambers. We also built disinfection chambers, which look quite different. We built such installations and knew what they looked like, even after the necessary installations. As a building firm, we often had work to do after installation of the machinery...
Question: When did you learn that your firm was supposed to have built gas chambers for industrial mass killing?
Answer: Only after the end of the war.
Question: Weren't you quite amazed about it?
Answer: Yes! After the war I made contact with my former boss in Germany and asked him about it.
Question: What did you learn?
Answer: He also only learned about it after the war, but he assured me that the Huta Corporation certainly did not build the cellars in question as gas chambers.
Question: Would building alterations be conceivable after the withdrawal of the Huta Corporation?
Answer: Conceivable, sure, but I would rule that out on the basis of time factors. After all, they would have needed corporations again, the SS couldn't do that on their own, even with inmates. Based on the technical requirements for the operation of a gas chamber, which only became known to me later, the building erected by us would have been entirely unsuited for the purpose in regard to the necessary machinery and practicable operation.
Question: Why didn't you publish that?
Answer: After the war, first, I had other problems. And now it is no longer permitted.
Question: Have you been interrogated as a witness in this matter?
Answer: No Allied, German, or Austrian agency has ever taken an interest in my knowledge of the construction of crematoria II and III, I or my other activity in the former general government. I was never interrogated in this matter, although my services for the Huta Corporation were known. I mentioned them in all my later CVs and recruitment applications. Since knowledge of the facts is dangerous, however, I never felt any urge to disseminate it. But now, when the lies are getting increasingly bolder and contemporary witnesses like myself are slowly but surely dying off, I am glad that someone is willing to listen and set down the way it really was. I have serious heart trouble and can die at any moment, it's time now.
Walter Schreiber (rest in peace) asked to publish this interview after his death for reasons known to us all.
Now, the two architects that designed the "gas chambers," Walter Dejaco and Fritz Karl Ertl. The two were put on trial in 1972 in Vienna for the murder of three million (!) Jews in crematorium II and crematorium III, but were acquitted because the court could not establish any connection between the two and the supposed mass murder in the "gas chambers." They both denied knowing what the buildings "were to be used for" (other than their intended use) and were released from custody on March 11th, 1972.
During the trial, a construction expert testified before the court:
Question: Do the plans indicate that these were gas chambers?
Answer: No.
Question: Could the accused infer from the plans that they could be transformed later into gas chambers?
Answer: No.
There you go, as clear as day. But nevertheless, let's move to the aerial photographs themselves.
First, the May 31st, 1944 photograph of crematorium II (on the left) and crematorium III (on the right):

Here's a close-up of crematorium II:
Many "believers" and revisionists alike were confused by this photograph, because there don't appear to be any smudges on the "gas chamber" at all, and all had their own explanations. However, the photo below paints a different picture:

The blue lines correspond to the actual (approximate; should be a little lower) edges of the "gas chamber" and there is indeed a smudge going in a single line (S1). Why the actual edges aren't visible is perhaps due to the lower quality of the scanned image, and this is the reason why some have mistaken the S1 and S2 lines as the edges. But then, what is the S2 smudge? We don't know. Nobody does. More so, what is the S3 line? Again, nobody knows. The S2 and S3 lines could be anything from shrubs, grass, logs, boards, pipes, ditches, building material, unassembled fence posts, etc. It's not really important. The marks F1, F2 and F3 are the (then) unfinished fences. The only important bit of information on this photograph is the S1 smudge, which the experts above have confirmed to be without elevation or shadows. The S1 smudge is, as the experts claim, discoloration of the roof.
Here are two ground photos for some perspective:

On the bottom left is the original photo from May 27th, 1944; above it is the same photo with the marked fences. The F2 side of the fence is marked with yellow, the F3 side with blue. On the right is a photo from roughly the same time, May 1944, perhaps even on the same day. Krematorium III has no fence, and Krematorium II only has part of it, as in the aerial photograph. Surely if this fence was meant as "camouflage," they wouldn't have left Krema III bare-naked like that, since both the crematoriums were active at the time. It was a simple additional barrier of no significance. Had it been intended as camouflage, it would have been one of the first things the Germans would build. Instead, they were supposedly "gassing" inmates for months without any camouflage at Krema III and only partial camouflage at Krema II. Why go on for months without finishing the "camouflage"? It's not exactly like building a skyscraper; it's a simple fence. Surely lack of "material" wasn't an issue, and the logistics behind building a fence aren't complicated at all. Untrained inmates could have done it, without involving any building corporation into it.
Next, the July 8th, 1944 photograph:

The quality of this photograph is lower than the others. Interestingly, it's the only one made by the Luftwaffe.
The main S1 smudge is still there, in a single line, but the S2 and S3 lines are not. There are faint outlines of the F1 and F2 fence visible, still unfinished. The bad quality of the photo has to do with their almost invisible appearance, which John Clive Ball concluded on his air-photo.com website to disappear completely. John Clive Ball believes the smudges and the fences are drawn on the photographs by the CIA, which is quite an extreme theory, since there is a different explanation altogether. In short, John Ball is wrong.
Next, the August 23rd, 1944 photograph:
The quality is bad, but should be no different than the August 25th image below, which is the best quality aerial photograph. Notice the F1 and F2 fences have been extended (completed). I'd also like to mention that the area below crematorium III is the Auschwitz
soccer field! That's right, the soccer field was right next to the gas chamber!
August 25th, 1944 photograph:
Notice the S1 smudge is no longer in a single line, but consists of four spots in different angles, all of which are located on the bottom (eastern) half of the roof. Their sizes are from 3 to 4 metres.
Their huge size might be clearer in the original 1979 report by the CIA:
Quite a size for a 'vent', since the 'eyewitnesses' claim they were around 70 centimetres in diameter and protruded around 60 centimetres from the roof. Let's remind ourselves that the experts above have confirmed these to be without elevation or shadows.
Next, September 13th, 1944:

Sometimes referred to as the "bombs photograph" because there is another frame showing bombs being thrown on the Monowitz camp in Auschwitz. On the crematorium II "gas chamber," only one of the four smudges is visible, with another fainter spot a little to the left of it. Again, the experts above have confirmed these to be without elevation or shadows.
The last photograph; December 21st, 1944:

The quality of this one from Pressac's book is quite low.
A close-up of crematorium II from a different source:

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Two of the four smudges are visible, with two or three fainter smudges to the left of them. All in all, this suggests more or less a consistency of the smudges, except for the difference in quality or some other factors that made the smudges more visible on some photos and less on others. Also, in the May 31st and July 8th photographs, the smudge is a single line, compared to the other photographs.
The four smudges on crematorium III appear to be more or less in similar locations in all the photographs. John Clive Ball claimed they in fact change, but again, he is wrong.
Now then, the question is,
what in the world are these smudges!?There are two possibilities:
Number 1 –
raveling (single 'l'). What is raveling? It's loss of material from the surface caused by ultraviolet exposure, rain, snow and moisture. This is very common on roads. Another term for this is
extractive bleed-through. And if I quote an engineering firm's website:
Extractive bleed-through stains are black streaks that run vertically down an asphalt shingle roof. These stains vary in width and length, but are a clear indication of a defective roofing product. Extractive bleeding occurs when an excessive amount of bitumen or black pigment is released from the asphalt shingles and runs down the surface of the roof. The defect is simply that the bitumen was not well bound in the asphalt mix during production. Since bleed-through stains are a characteristic of the asphalt shingles themselves and not from an exterior source, the discoloration will probably manifest over large areas of roof.
The good news about extractive bleed-through is that it is a product defect described by manufacturers as cosmetic and should not affect the integrity of the roof. The unfortunate news is that there is not much to do to remedy bleed-through stains because power washing and chemical treatments can reduce the remaining useful life of the roof.
Basically, the surface is damaged and bitumen leaks through. This can be observed on the collapsed roof of crematorium II:

Even today:

The example above was caused by the explosion, however.
Here is an example of a sidewalk in Santa Rosa, California:
Number 2 –
algae, fungi, moss, lichens or grass. Let me quote the same engineering firm:
Algae and fungi typically appear as black spots or streaks, varying from what appear to be faint shadows to dark stains. Moss and lichens are greenish and appear to be more of a growth than a stain. All of these building detriments are common on roofs that are subject to little sunlight and high humidity.
Mold is a type of fungus supported by the carbon released during the decomposition of other organisms such as leaves or sticks left on a roof. Algae are plants that use photosynthesis and are supported by moisture in inorganic material such as the calcium carbonate found in the limestone particles of asphalt shingles. Mosses are small soft plants and lichens are composite organisms consisting of fungus and algae. While inherently different, mold, algae, moss and lichens thrive in warm humid environments and normally appear on the northern slope of roofs where shade and moisture are often found. These organisms occur naturally and are hard to prevent. In fact, algae and fungal growth used to be limited to warm and humid climates, but can now be seen on rooftops as far north as Canada.
Remember, the experts have confirmed the smudges are neither shadows, nor do they have any elevation. They are simple discolorations, caused by either the bitumen leaking through or by moss or fungi growing on the roof.
As for the actual holes in the remains, Pressac and van Pelt found none. Professor van Pelt believes the Germans poured cement over the holes, waited for it to dry and
then blew up the building. Genius!
Charles D. Provan found
8 holes out of which he considers three (
2 (Mazal's hole number 1), 6 (Mazal's hole number 2), 8 (disregarded by Mazal)) to be original. The others are too small, are simple cracks or were made after 1945.
There was a thorough inspection of the crematoria from May 12th to June 4th in 1945 by the Poles, but they did not mention any holes in the roof, as the holes were not there yet.
Hole number 2 was made by the Poles or Soviets sometime after the inspection. Why? Because the roof lacked 'criminal holes'. This hole has also been increased between 1990 and 1997 with a chisel, as shown by Carlo Mattogno in his No Holes, No Gas Chamber(s) report. Even though it was increased, it is still not wide enough to be considered an insertion hole. Supposedly the insertion holes were 70x70 centimetres. This hole was 86 cm long with 50 cm at the widest and 43 cm at the narrowest side in 1990, as measured by Carlo Mattogno. That's a problem for the "believers."
Provan believes that
hole number 7 could not have been an insertion hole because iron bars were in the way! In 1992, there were 5 iron bars present, in 1997, only two remained, in 2000, only one! In 2011? Who knows, perhaps an additional hole? What's going on? Did gypsies come and steal old metal!? Not only did the metal bars disappear, it was chiselled into a crude square-like shape.
Holes number 7 and 2 were made in 1945 to make them look like Zyklon-B insertion holes.
Hole number 6 is a simple crack like
holes number 1, 3, 4 and 5 caused by the collapse of the roof. It has no shape at all.
Hole number 8 is again a simple crack caused by the collapse of the roof. It even has four iron bars sticking out. For photographs, look up Carlo Mattogno's report mentioned below!
Mazal's hole number 3 is not visible at all. The authors presume the hole is under the rubble and therefore couldn't locate it!
Mazal's hole number 4, which would make Provan's hypothetical
"hole number 9" (or 10) had he noticed it, is yet another crack in the roof. Pressac and van Pelt both excluded this hole and the rest of Provan's cracks and the two Soviet-made (2 & 7) holes as possible Zyklon-B introduction holes.
Here's the drawing from above, this time with two grey and two green marks:

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The green marks are the positions of the two objects on the "train photograph." At neither of those locations is there a hole in the roof. The grey mark on the right is Provan's hole number 2 (Mazal's hole number 1). The one on the left is Provan's hole number 7. Here's what Mazal and his ilk had to say about this hole: "
Hole cut for unknown purpose in Crematorium II roof, likely after liberation in January 1945."
Unknown purpose? To the believers, perhaps, but they're lying to themselves.
In short, all the holes that can be found are irregularly shaped, show no crafted edges, are in the wrong locations, are of the wrong dimensions (including holes number 2 and 7 above) and some have iron bars sticking out of them. There are also no remains of any chimneys or any other protruding objects.
As for crematorium I in Auschwitz, it was converted into an air-raid shelter sometime after September 21st, 1944.
Here's an aerial photograph from April 4th, 1944:
Here's one from August 25th, 1944:
Notice no holes or vents on the roof, except for the two chimneys which even "believers" will tell you had nothing to do with Zyklon-B insertion holes or the "gas chamber" in general. The number of holes also varies; Rudolf Höss -
one, Stanisław Jankowski and Hans Stark -
two, Jean-Clause Pressac -
three, Soviet commission for investigation -
four, Mazal, Keren and McCarthy -
five, Pery Broad and Filip Müller -
six, Czesław Sułkowski, who supposedly made the holes himself and saw Russians being gassed -
didn't know how many holes there were!
There is also a photo in Pressac's book:

where there are supposedly three (four according to Mazal, with originally
five(!) holes) black marks where the holes used to be (and later sealed), over which the Soviets "reconstructed" the vents. Here's what Pressac has to say:
This photograph proves that a dance was organized in 1945 on the roof of Krematorium I, and that people actually danced above the homicidal gas chamber. This episode appears almost unbelievable and sadly regrettable today, and the motives for it are not known.
Party on the roof of a building where thousands were supposedly gassed, how nice of the Soviets!
In reality, none of the reconstructed vents are in any of those locations! For more on this, look up
"The Openings for the Introduction of Zyklon B - Part 1: The Roof of the Morgue of Crematorium I at Auschwitz" by Carlo Mattogno or
"Auschwitz: Crematorium I and the Alleged Homicidal Gassings, chapter 6, The Openings for the Introduction of Zyklon B: Material Evidence" by Carlo Mattogno.
Now, to finish this with a quote by A. S. Marques from a letter to Zündel:
It appears, therefore, that the existing holes that can be found are false and the non-existing holes that cannot be found are true.
And remember,
NO HOLES, NO HOLOCAUST!