When in the summer of 1941 he (Hitler) gave me the order to prepare installations at Auschwitz where mass exterminations could take place, and personally to carry out these exterminations, I did not have the slightest idea of their scale or consequences. It was certainly an extraordinary and monstrous order. Nevertheless the reasons behind the extermination programme seemed to me right. I did not reflect on it at the time: I had been given an order, and I had to carry it out. Whether this mass extermination of the Jews was necessary or not was something on which I could not allow myself to form an opinion, for I lacked the necessary breadth of view.

Quoted in "Commandant of Auschwitz: The Autobiography of Rudolf Hoess" - Page 144 - by Rudolf Hoess, Constantine Fitzgibbon, Primo Levi, Joachim Neugroschel - History