How do we know the documents about the existence and use of the gas vans are authentic?
Holocaust deniers claim:
The Becker-Rauff letter, a key primary German document that explicitly discusses the construction and use of gas vans is “not credible” and of “dubious origin.”
The facts are:
The Becker-Rauff letter is not “uncertain,” “dubious” or forged. The testimonies of the men who wrote the letter and who built and used the gas vans—August Becker, Walther Rauff, and Otto Ohlendorf—corroborate its authenticity.
Ingrid Weckert, a German Holocaust denier, claims that a detailed letter about the existence and use of the gas vans in the occupied Soviet territories is a forgery created by the Allies for the International Military Tribunal for the Trial of Major German War Criminals in 1945/46.
The facts about the Becker-Rauff letter.
The letter is dated May 16, 1942 and is from August Becker, a chemist, to Walther Rauff, the head of the gas vans program in Berlin. Rauff had sent Becker to the East to investigate problems relating to the gas vans and report back him. In the letter Becker refers to “places of execution,” “persons to be executed,” the need to camouflage the vans as observers have begun calling them “death vans,” and how leaks were endangering the health of the drivers.
Weckert attempts to discredit the Becker-Rauff letter by citing an affidavit Rauff gave to his American captors in 1945. In it Rauff affirmed that he was the head of the department that constructed the gas vans from February 1940 to March 1940 and then again from May 1942 to June 1942. However, Rauff claimed that during the period between March 1940 to May/June 1942 (when the gas vans were built and used), he was assigned to other tasks so ultimately he had no knowledge of the building or use of gas vans. Based on this affidavit, Weckert claims that Becker’s letter is a forgery because Rauff was not the head of the department that built them during that time.
However, in 1972 Rauff gave another affidavit in the German embassy in Santiago, Chile on behalf of one of his colleagues then on trial in Germany. Rauff was captured by the Americans in Italy after the war. He escaped their custody and fled to Damascus, Syria. From there he moved on to Ecuador and finally settled in Chile, where he worked as the manager of a king crab cannery until his death in 1984. Weckert characterizes this chain of events as Rauff’s “emigrating” to Chile.  Chile had refused to extradite Rauff to Germany many times before and he did not fear that possibility in 1972. The affidavit was proofed and signed by him.
In his second statement, Rauff said: “Regarding the annihilation of Jews in Russia I know that gas vans were used for this purpose . . . I saw two of these vans standing in the yard, which Pradel [Rauff’s subordinate] showed me . . . the gas vans were used for the execution of sentences and the killing of Jews.” Rauff also admitted in the second affidavit that he had headed the department in the time period in which the gas vans were designed, built and used.
On October 18, 1945, when Rauff was interrogated in captivity In Italy by the Americans, he was presented with the Becker letter and asked to confirm its authenticity. He wrote a note on the left margin of this letter confirming its authenticity. Further, in an affidavit voluntarily given on June 28, 1972 he stated. “. . . I received something from Becker about the use of gas vans. I myself had told Becker to send me a corresponding report.”
The testimony of Otto Ohlendorf.
Otto Ohlendorf, the head of Einsatzgruppe D (the mobile killing units in the occupied Soviet territories), testified at the International Military Tribunal for the Trial of German Major War Criminals in 1945/46. In his testimony before the court, Ohlendorf stated that he had received the gas vans in the spring of 1942 for use in the “killing of women and children” and that Becker had visited his unit to supervise their use.
Ohlendorf’s testimony also corroborated the information in German documents about the design of the gas vans. He stated that the gas vans could not be distinguished from any other truck on the outside but they were “constructed [so] that when the motor ran, the gas was conducted into the van causing death of the occupants in 10 to 15 minutes.”
The Becker-Rauff letter is not “uncertain” or “dubious” as Weckert claims and it is not forged. The testimonies of the men who designed, built and used the gas vans corroborate its authenticity.
By Photographer: Schwarz; Colors added by Tzo15 [CC BY-SA 3.0 (http://creativecommons.org/licenses/by-sa/3.0)], via Wikimedia Commons
 Ingrid Weckert, “The Gas Vans: A Critical Assessment of the Evidence” (“3.1.4. Summary”) and (“3.1.1. Origin of document PS-501”) at http://www.vho.org/GB/Books/dth/fndwagon.html.
 Ingrid Weckert, “The Gas Vans: A Critical Assessment of the Evidence” (“3.1.4. Summary”) and (“3.1.1. Origin of document PS-501”).
 You may read the entire text of the Becker/Rauff letter at http://holocaustresearchproject.org/einsatz/rauff.html.
 Ingrid Weckert, “The Gas Vans: A Critical Assessment of the Evidence” (“3.2 Affidavits”).
 Santiago Alvarez and Pierre Marais, The Gas Vans: A Critical Investigation (Barnes Review, 2011), p. 288.
 You can read the entire text of Rauff’s 1972 deposition (p. 12) at http://www.nizkor.org/ftp.cgi/people/r/rauff.walter/Rauff-deposition-translation.
 You can read the text of Ohlendorf’s testimony about the use of gas vans on the Eastern Front (Part 4 of 15) at http://www.nizkor.org/hweb/imt/tgmwc/tgmwc-03/tgmwc-03-26-04.html.