According to Hanns and Rudolf by Thomas Harding near the end of WW2 the allies created a large database ... known as CROWCASS, of war criminals which they intended to target once victory was achieved.
Rudolf Hoess was listed with his name spelt slightly wrong, and his age and other details slightly off. However the list did identify him correctly as commandant at Auschwitz.
How easy would it have been for allied agents in in Berlin to obtain this kind of information? Were Nazi "H.R." type records within allied reach - via spies - during the war? Presumably Auschwitz was a fairly secret project and you couldn't just thumb a public directory or follow the news in order to learn the personal details of Auschwitz's commandant.