Allied officials gathered news about Nazi terror from different sources, such as intercepted SS messages and interrogations with German POWs. Even more vital information came from escaped prisoners. The most important survivor account was written by two Slovakian Jews, Rudolf Vrba and Alfred Wetzler, following their escape from Auschwitz in April 1944. Vrba and Wetzler wrote in detail (using somewhat inflated figures) about the mass extermination of Jews in Birkenau. Within months, copies of their report had reached various Allied governments, as well as the Vatican and the World Jewish Congress. Details were also published in the Allied media in 1944. Growing knowledge about the Holocaust did not alter the course of the war: Allied leaders focused on military strategy, not humanitarian missions. But it did affect public opinion in Allied nations, silencing those who had doubted earlier reports about mass extermination in Nazi camps.
In the first detailed report by a United States government agency offering eyewitness proof of mass murder by the Germans, the War Refugee Board [WRB] made public today accounts by three persons of organised atrocities at Birkenau and Oswiecim (Auschwitz) […].
The gassing takes place as follows
The two Slovak youths [Rudolf Vrba and Alfred Wetzler] cited in the WRB reports estimated the number of Jews gassed and burned at Birkenau in the two-year period at 1,765,000 […]. In the report the Jewish youths described the gassing and burning technique as follows: “At present there are four crematoria in operation at Birkenau […]. Next to this is the large ‘reception hall’, which is arranged so as to give the impression of the antechamber of a bathing establishment. […] From there a door and a few steps lead down into the very long and narrow gas chamber. The walls of this chamber are also camouflaged with simulated entries to shower rooms in order to mislead the victims. […]. The gassing takes place as follows: The unfortunate victims are brought into the hall, where they are told to undress. To complete the fiction that they are going to bathe, each person receives a towel and a small piece of soap issued by two men clad in white coats. Then they are crowded into the gas chamber in such numbers that there is, of course, only standing room. […] When everybody is inside, the heavy doors are closed. Then there is a short pause, […] after which SS men with gas masks climb the roof, open the traps, shake down a preparation in powder form out of tin cans labelled ‘Cyklon’, for use against vermin, which is manufactured by a Hamburg concern. It is presumed that this is a ‘cyanide’ mixture of some sort which turns into gas at a certain temperature. After three minutes everyone in the chamber is dead.”
Source: “US Board Bares Atrocity Details Told by Witnesses at Polish camps”, New York Times, 26 November 1944