Previously a bricklayer by trade, Theuer's SS career began when he enlisted in the
Waffen-SS in 1938 after the
Nazi invasion of Czechoslovakia. He was deployed to Auschwitz in 1940 at the rank of SS-
Rottenführer. On 1 August 1941 he was promoted to SS-
Unterscharführer. He served as an SDG or
Sanitätsdienstgefreiter; a medical orderly as part of the
Sanitätswesen, one of the five concentration camp departments involved in running such a facility. He was also a member of the
Desinfektionskommando (disinfection command), the unit of SS medics involved in the mass gassing of prisoners. One of Theuer's responsibilities was inserting the
Zyklon B into the
gas chamber, a task shared by other SS orderlies such as SS-
Unterscharführer Hans Koch and SS-
Oberscharführer Josef Klehr. During the
Frankfurt Auschwitz Trials, Klehr, the chief of the
Desinfektionskommando, testified that Theuer explained to him that he would insert the gas when ordered to do so by the accompanying SS doctor. SS-
Unterscharführer Oswald Kaduk recalled an incident when Theuer, his fellow
Upper Silesian countryman, was reluctant to insert the gas. Kaduk stated that: During the
Frankfurt Auschwitz trials in the 1960s, Edward Pys, a survivor of Auschwitz, also recounted a gassing done by Theuer: Theuer remained at the camp until its evacuation in January 1945, when he was subsequently deployed in
Ohrdruf concentration camp, a subcamp of
Buchenwald concentration camp. He was tasked with murdering sick prisoners. ==Post-war==