It's anti-Semitic propaganda of the worst kind. You should have researched this yourself. I don't have time to give you a history lesson so I'll make this quick:
1) Allies knew about camps by late 1942.
2) Near the war's end Himmler contacts allies and says if they give him trucks for the eastern front he'll stop shipping Jews to the extermination camps.
3) Allies who liberated camps found fucking warehouses of millions of shoes and other belongings and filmed them.
3) Allies found thousands of dead stacked like cordwood and rotting corpses and emaciated(starved) survivors. They filmed all this too.
4) Allies found that at Birkenau the wife of the camp commander had been making fucking lamp shades from human skin.
5) Allies were so fucking horrorfied and disgusted they made Germans in villages around the camps bury the thousands of dead that were still lying around everywhere. They made them visit the camps and see the fucking lampshades and other horrors. In one town the mayor and his wife went home and hung themselves.
6) Allies film gas chambers and ovens.
7) Allies get official state records showing the exact numbers of people and dates for the train schedules.
8) The allies find the cyanide gas cannisters, gas chambers, the official train schedules and other documents, witnesses from the camps, SS guards and other Germans involved who they interrogated, the warehouses full of personal belongings etc. They also found that more than 3/4 of all European Jews were no longer around.
The actual original architectural blueprints showing the gas chambers and crematoriums at Auschwitz/Birkenau: