1943 In a speech to SS Generals at Poznan, Heinrich Himmler, Reich Leader (Reichsführer) of the SS (Schutzstaffel; Protection Squadrons), remarks that the mass murder of the European Jews will be kept secret, never to be recorded.*
Which just shows you the level of intelligence the Nazis were working with.
“Hey, you guys took over Europe and millions of Jews living there just vanished! What happened to them?”