"As far as the consequences of Himmler's racial theories, I have, from personal observation and experience, nothing to say. Hitler and Himmler succeeded in keeping this part of their programme strictly secret. Himmler's 'methods of education,' as practised in the concentration camps, have meanwhile become sufficiently well known. During his lifetime the general public knew only a little about this. The atrocities carried out in those camps were made known to most people, as to myself, only after the collapse. The way the concentration camp methods were kept secret can only be described as masterly."
January 1, 1970
https://en.wikiquote.org/wiki/Heinrich_Himmler