Holes on Krema I's roof, and their correspondence to the building's interior
Let's look at the bottom part of the above image first. What we see here, is Eric Hunt's 3D model of roughly half of Krema I. It covers (from left to right) the "storage for spare gratings" room, the wash room, the gas chamber, and the vestibule.
When Krema I was partially reconstructed in 1947, 4 interior walls were knocked down (2nd, 3rd, 4th and 5th from left to right). The Soviets made two mistakes: one, knocking down the 2nd wall, as this was the actual gas chamber wall rather than the 1st (which is the wall between the store room and the wash room where a wooden door is located). And the second "oddity" (I wouldn't say mistake) they made is leave the vestibule to the right intact, as this is not on the 1942 blueprint and was part of the efforts (along with the 3rd, 4th and 5th interior wall that are also missing on the blueprint) of the Nazis to convert the building into an air-raid shelter with the additional walls reinforcing structural integrity.
Holocaust deniers say, that if you leave the first two walls (from left to right) intact and remove the 3rd, 4th and 5th wall as well as the vestibule to get the original gas chamber configuration, you end up with holes in the ceiling that are not spaced out properly (they are if you knock down the 2nd wall and consider the 1st wall as the gas chamber wall, i.e. the way the interior looks today, but which is false). They tout this as proof that these holes were not placed there by the Germans and instead are a Soviet invention, with the Soviets' dumb mistake of knocking down one wall too many interior walls leading to them spacing out the holes wrongly, and therefore getting caught by our revisionist heroes some decades later.
This conclusion deniers make would indeed have made sense IF one of the holes today were to be found OUTSIDE the borders of the morgue that ended up being the gas chamber - except that isn't the case. What we have instead, are all four holes located exactly on the morgue roof, except they aren't as symmetrically spaced as people suffering from Obsessive-compulsive Disorder would like them to have been.
Now while I personally am leaning toward a 3-hole configuration having been the historical case, the 4-hole configuration is still anything but far-fetched. Let me explain: this asymmetry makes sense, given that the Krema I gas chamber is the only gas chamber in the entire Auschwitz-Birkenau camp complex to have had two gas chamber doors in close proximity to each other: placing an additional zyklon hole close to the two doors would ensure higher initial levels of HCN lethality near said doors to prevent the trapped from trying to break these open.
I do not try to exculpate the Soviets from their shoddy reconstruction work, however. Because knocking down the original gas chamber wall while leaving the vestibule intact, and making a wrong entrance to the crematorium that does not align with the tracks anymore is shoddy restoration work indeed.
Now let's take a look at the roof. There's a whole bunch of stuff here, so bear with me. We have two smaller chimneys above the crematorium section of the building. And of course the 4 zyklon-b inlet holes poking through the roof and protected from the elements by square-shaped wooden covers (for a closeup, see top right). We also have two smaller chimneys in between (3rd row of chimneys going away from us from left, in the centre top of the above image).
The Nazis sealed up the vents when they converted the building to the air-raid shelter, and the smoothness of the roof indicates the Soviets didn't miss these and drill in the wrong place. The only question then, is if the Soviets drilled too many holes, as eyewitness accounts indeed vary regarding the exact number of zyklon-b vents on the roof of Krema I. There definitely were two, three is a reasonable estimate, though four is a bit less likely. Given that the gas chamber of Krema I is much smaller than that of e.g. Krema II or III in Birkenau (and those used to have 4 inlet holes each, as I will show air photos indicating this later on), I do agree that 4 holes on Krema I's roof seems a bit much.
