The Holocaust was well-documented by the extremely bureaucratic German government itself. It was further witnessed by the Allied forces who entered Germany and its associated Axis states towards the end of World War II. Among the evidence produced was film and stills that showed the existence of prisoner camps, as well as the testimony of those freed when the camps were entered. The Holocaust was a massive undertaking that lasted for years and was implemented across several countries, with its own command and control infrastructure, a bureaucracy that left a large trail of documentation. Although Nazi officials made attempts to destroy evidence of the Holocaust when it became evident that their defeat was imminent, substantial documentation remained. After the Nazi defeat, many documents were recovered, including numerous reports written by the Nazis about the number of Jews killed, records of train shipments of Jews to the camps, orders for tons of cyanide and other poisons, and large numbers of photographs and films of the camps and their victims. Many thousands of not-yet-decomposed bodies were found in mass graves located near facilities that were indisputably concentration camps. Thousands of interviews with survivors, perpetrators, and bystanders added to the massive level of documentation that attended the Holocaust. A diary written by German anti-Nazi Friedrich Kellner attests that some atrocities, such as the murder of Jews at gunpoint, were indeed committed by German soldiers, but also illustrates that an awareness of such crimes was present among some German anti-Nazis.
Aerial photographs of Auschwitz indicate that what appears to be ash produced in Auschwitz was piled into the nearby river and marsh, and there is well-documented evidence that other ash was used as fertilizer in nearby fields. Photographs of Treblinka taken by the camp commandant show what looks to be ash piles being distributed by steam shovels.
Holocaust deniers often ignore the documents produced by the Nazis themselves, who used figures of between 9 and 11 million for the Jewish population of Europe, as evidenced in the notes of the Wannsee Conference. In fact, the Nazis methodically recorded the ongoing reduction of the Jewish population, as in the Korherr Report, which gave the status of the Final Solution through December, 1942:
The Nazis themselves documented many of their crimes. The Höfle Telegram was sent by SS-Sturmbannführer Hermann Höfle on January 11, 1943 to SS-Obersturmbannführer Adolf Eichmann in Berlin and detailed the number of deaths of Jews in the concentration camps. In the year 1942 alone, the telegram lists 1,274,166 Jews were exterminated in the four camps of Akton Reinhard. The Korherr Report compiled by an SS statistician, gave a conservative total of 2,454,000 Jews deported to extermination camps or killed by the Einsatzgruppen. The complete status reports of the Einsatzgruppen death squads were found in the archives of the Gestapo when it was searched by the U.S. Army, and the accuracy attested to by the former Einsatzgruppen members who testified during war crime trials and at other times. These reports alone list an additional 1,500,000 or so murders during mass shootings, the vast majority of these victims were Jews.
Holocaust deniers discount the testimony of officers claiming that these witnesses were tortured, or that Rudolf Hoess allegedly signed a confession written in a language he did not understand (English) or that the Nuremberg Trial did not follow proper judicial procedures. However, Hoess's testimony did not consist of merely a signed confession; he also wrote two volumes of memoirs before being brought to trial and gave extensive testimony outside of the Nuremberg proceedings. Further, his testimony agrees with that of other contemporary written accounts by Auschwitz officials, such as Pery Broad, an SS man stationed at Auschwitz while Hoess was the commandant and the diary kept by SS physician at Auschwitz Johann Kremer, as well as the testimony of hundreds of camp guards and victims.