First and foremost, there are testimonies, affidavits and depositions – by victims, witnesses and perpetrators – at numerous Holocaust-related trials (unfortunately, there was no “Holocaust Trial”).
More specifically, at the Einsatzgruppen trial (in 1947 in the American-occupied Nuremberg), the “Death Camps Trials” (Auschwitz, Treblinka, Belzec, Sobibor, Chelmno) in early 1960s in West Germany and the trials of individual war criminals (the most famous being obviously the Eichmann trial in Jerusalem in 1961).
Unlike at the “main” Nuremberg trial of Third Reich leaders in 1945-46 (which was a political endeavor, not legal), the prosecutors and judges at these trials went to great lengths to ensure that the proceedings meet the highest standards of criminal justice.
Consequently, there is no doubt whatsoever that the defendants (the perpetrators), the victims and the witnesses told the truth, the whole truth and nothing but the truth. And this truth does fully and completely confirm the facts about The Holocaust listed above.
Second, there are numerous Nazi documents related to the design and construction of gas chambers (see for example an excellent work by Jean-Claude Pressac on Auschwitz gas chambers), deportations to death camps (Höffle Telegram, Korherr Report, etc.), the affidavit by Kurt Gerstein (on gassing of Jews in Belzec death camps), August Frank memorandum, etc. that prove beyond the reasonable doubt the existence and operation of death camps, gas chambers and gas vans.
Third, the documents and testimonies on the layout and structure of Chelmno, Sobibor, Treblinka and Belzec camps prove beyond the reasonable doubt that these facilities could be only death/extermination camps – and nothing else. Besides, the abovementioned Nazi documents (as well as many others) demonstrate – again beyond the reasonable doubt – that the “ticket” to any of these places was strictly one way.
In other words, while hundreds of thousands of Jews went in, just about no one got out (with the exception of a very small number of Jews transferred to slave labor camps).
Fourth, all commandants and key staff of the abovementioned camps came from the Aktion T4 euthanasia program. In other words, they all had extensive experience in mass murder of human beings (ultimately the project claimed over 70,000 lives in two years)… in stationary gas chambers. Which makes sense only if these camps were death camps where victims (i.e. Jews in this case) were to be murdered in gas chambers (using carbon monoxide).
Fifth, the Yad Vashem memorial (the World Holocaust Remembrance Center in Jerusalem) initiated and operates “The Central Database of Shoah Victims’ Names” project.
This project has a highly ambitious (and IMHO unrealistic) objective – to compile a complete list of all victims of The Holocaust. Identifying every victim by name and putting an end to the debate about the total number of victims of the Shoah.
Being aware of the vicious efforts of all sorts of “Holocaust deniers”, the staff of this project makes sure that their efforts adhere to the highest professional standards of historic research and search for missing persons. Consequently, although their database is not exactly perfectly accurate (to put it mildly), it still contains sufficient information to prove the statements listed above beyond the reasonable doubt.
Sixth, the minutes of the Wannsee conference prove (again beyond the reasonable doubt) that one of the ways to implement the “Final Solution to the Jewish Question” is so-called “extermination through labor” (in other words, literally work the able-bodied Jews to death).
These minutes also quite openly state that those Jews who survive, will be murdered so as not to create the core of “Jewish resistance”. Another proof that the Wannsee Conference was about extermination of Jews is who was present at the conference (SS Major Rudolf Lange). And who were not (Wehrmacht generals).
In November 1941 (roughly two months before the Wannsee Conference) Lange was responsible for planning and carrying out the murder of 24,000 Latvian Jews from the Riga ghetto which occurred on 30 November and 8 December 1941.
This monstrous crime has come to be known as the Rumbula massacre and became the biggest two-day Holocaust atrocity until the operation of the death camps. And though Wehrmacht generals generally supported murderous activities of Einsatzgruppen (including killing the Jews which the German military brass viewed as horrible but necessary component of “pacification” of occupied territories), a wholesale murder of ALL European Jews was a different matter entirely. Worthy of a military coup even.
Contrary to a (very) popular misconception, nothing that Adolf Hitler ever said proves beyond the reasonable doubt that he gave the order to murder all Jews of Europe. His commonly quoted statements on this issue can be easily dismissed as “all bark, no bite” (which is very common among charismatic dictators).
SS-Reichsfuhrer Heinrich Himmler was a different character entirely. He was not a politician – he was a leader of an extremely powerful (almost omnipotent) police, security and paramilitary force in the Third Reich. Consequently, his statements carried a much more serious weight – as he meant what he said, walked what he talked and practiced what he preached.
In his now (in)famous Posen speech on October 4th, 1943 (at the end of Operation Reinhard) to about 100 SS generals, Himmler explicitly acknowledged the genocide of the Jews:
“I am now referring to the evacuation of the Jews, the extermination of the Jewish people… Most of you here know what it means when 100 corpses lie next to each other, when there are 500 or when there are 1,000. To have endured this and at the same time to have remained a decent person… has made us tough, and is a glorious chapter that has not and will not be spoken of…”