On August 8, 1942, Gerhart Riegner, who then worked in Geneva as the secretary of the World Jewish Congress, sent a telegram to contacts in the U.S. State Department and the British Foreign Office informing them in some detail about the systematic murder of European Jewry. Walter Laqueur explains how Riegner came to this information, why those in positions of power ignored it, and what the Western Allies might have done had they chosen to act on the information:
[In mid-1943], hundreds of thousands of East European Jews were still alive—the Łódź ghetto was still in existence, as was the Kovno ghetto, and half-a-million Hungarian Jews were still alive. If a somewhat higher priority had been given to saving these remnants, tens, perhaps hundreds of thousands of Jews could have been saved. . . .
In 1944 hundreds of thousands of Hungarian Jews were still alive. It has been suggested that the idea that Auschwitz could have been bombed is tantamount to Monday-morning quarterbacking, that the difficulties were great, that many of the inmates of the camps would have been killed. However, the transports to Auschwitz would have stopped for a certain period of time, perhaps a long period if the attacks had been repeated . . . and this at a time when the Allies from East and West were advancing rapidly.
If no such attacks were made, it was not because it was deemed technically impossible, but because the fate of those concerned had very low priority. The issue of bombing quite apart, yet another aspect of this situation was seldom discussed. The victims of the deportations were not quite aware of their fate, which was certain death in the gas chambers. Had they known this, it is almost certain that at least some would have tried to hide or escape. . . .
Allied radio stations had a near-monopoly in many of the regions [where there were still Jews, and] . . .broadcasting was not the only means of issuing warnings. But no such warnings were given. No one can say how many lives would have been saved; all we know is that the attempt was not made.
Read more on Tablet: http://www.tabletmag.com/jewish-arts-and-culture/books/192421/riegner-cable-shoah