From 1 April 1936, he was commandant of Bad Sulza concentration camp.[2] Between 1 August 1937 and mid-1938, Sauer was second Schutzhaftlagerführer in Sachsenhausen concentration camp and thus belonged to "Wachtruppe Brandenburg".[2] In the period between 1 August 1938 and 1 April 1939, he officially acted as commandant of the then-temporary quarry Wienergraben, so named because of the Wienergraben Valley in which it was located, of Granitwerke Mauthausen, which relied on slave labor from the subcamps of Mauthausen-Gusen.