In April 1942, Müller was ordered to Auschwitz concentration camp, where until June 1942 he served as Kompanieführer of the 1st Wachkompanie (First Guard Company). From July 1942 to October 1943, he served as Kompanieführer of the 2nd Wachkompanie in the main camp and was at the same time Schutzhaftlagerführer of the women's camp in the main camp, which, in August 1942, was converted into the extermination camp of Auschwitz-Birkenau (Auschwitz II). In the women's camp, he worked with OberaufseherinnenJohanna Langefeld and, from October 1942, Maria Mandl.[3]
In August 1943, he was replaced as Schutzhaftlagerführer in the women's camp by Franz Hössler.[4] In November 1943, he was Kompanieführer of the 1st and 2nd Wachkompanies in Monowitz concentration camp, which were also responsible for guarding the subcamps of Golleschau and Jawischowitz.[3] On 30 January 1944, Müller was awarded the War Merit Cross Second Class with Swords. In September 1944, he became head of the newly established satellite camp at Neustadt in Oberschlesien (now Prudnik, Poland). It was a weaving mill in which 400 female prisoners were forced to work. He served there until the evacuation of Auschwitz in January 1945.[2][5]
Lasik, Aleksander (1999). "Die Organisationsstruktur des KL Auschwitz". In Lasik, Aleksander; Piper, Franciszek; Setkiewicz, Piotr; Strzelecka, Irena (eds.). Auschwitz 1940-1945. Studien zur Geschichte des Konzentrations und Vernichtungslagers Auschwitz (in German). Vol. Band I - Aufbau und Struktur des Lagers. Oświęcim: Auschwitz-Birkenau Memorial and Museum. ISBN83-85047-87-5.