No autopsies of bodies were ever conducted by any Allied investigators to prove gassings of camp inmates.
No photographic evidence was taken by Allied aerial reconnaissance of the camps between 1942-1945 showing mass exterminations or removal of human remains, even though such activity would have been easily spotted.
No German communications, which were being monitored by the British government throughout the war due to the early cracking of German codes, alluded to any mass extermination or extraordinary loss of life in the camps.
No captured diaries or journals of high-ranking German officials alluded to any program of extermination, nor is there any documentation whatsoever alluding to a program of extermination. As holocaust believers claim that the National Socialists killed eleven million people - roughly 5 million Europeans and 6 million jews - the idea that every single document alluding to this massive operation was destroyed is ludicrous.
Neither mass graves of eleven million bodies nor the remains of the equivalent number of bodies in layers of ash and crushed bone, have ever been located in or around the internment camps.
The claims of 'human soap', 'skin lampshades', and 'shrunken heads' were debunked and admitted as lies in mainstream American newspapers in the 1980's.
The 'steam chambers' and 'electrified floors', the first alleged methods of mass extermination, were quickly proven to be lies before the 'gas chamber' story emerged and took hold in the public consciousness. If the gas chambers had been real, there would have been no need to lie about 'steam chambers' and 'electrified floors' initially.
The Katyn Massacre, the shootings of over 20,000 Poles for which Germans were hanged, was admitted by the Russian government in 1990 to have been actually committed by the Bolshevik NKVD.
The Babi Yar massacre was a lie conjured up by the Soviet jewish propaganda minister Ilya Ehrenburg. The story, which involved the Germans allegedly killing 30,000 jews outside of sniper-infested Kiev in 1941 (with no eyewitnesses) and then returning to the site three years later to dig up all the remains and destroy them using "bone-crunching machines" (while being pursued by the Red Army, no less) was laughable to begin with. However, there is evidence which supports mass executions of Ukrainians at the site in the early 1930's by the NKVD (see: Holodomor). It's probable that, like Katyn, the Babi Yar massacre was an example of the Soviets projecting their own atrocities onto their enemies as propaganda.
Official Soviet policy was to prioritize the evacuation of jews via trains ahead of the German advance. Eastern Soviet territories such as Kasakhstan, Uzbekhistan, and Tajikistan recorded huge numbers of jews flooding into their lands during WWII
All the "information" on gas chambers came from the Soviet Union, as the Western Allies did not capture any camps that are currently claimed to have had any, though initially, they did falsely claim that they had liberated "death camps" with gas chambers in them such as Dachau.
All German camps had supplies of Zyklon B, not just the camps which were said to have had gas chambers. Large quantities of Zyklon B are neither mysterious nor sinister, as it takes a relatively high amount of the spray to kill lice.
A study conducted in 1999 by an Australian team of researchers using ground-penetrating radar proved that the ground around Treblinka had been undisturbed down to 30 meters, meaning that no human remains of one million people were deposited there. This supports official German documentation which shows Treblinka to be a transit camp.