Mueller began working at the Munich police headquarters in December 1919. The Beginnings of Mueller's Association with the Nazis. Soon after Reinhard Heydrich became the Bavarian police chief, Mueller became one of his most important aides. His reports also gained Heinrich Himmler's attention, which won him promotions. In 1935, he was appointed controller of the criminal police. To ensure that no problems arose in the relations between the Bavarian political police and the Gestapo and SS, Mueller, who was not a party member, was in 1936 appointed a member of the SD (Sicherheitsdienst; Security Service), with the rank of Untersturmfuehrer.
Chief of Subsection II of the Gestapo
When Heydrich was appointed Gestapo chief, he took Mueller along with him, appointing him and Gerhard Flesch joint directors of subsection II 1 (suppression of hostile elements - including Jews). Flesch and Mueller, for their part, brought along experienced associates from Munich, such as Josef Meisinger, Franz Josef Huber, and, at a later date, Friedrich Panzinger.
The Path to Gestapo Chief
Mueller's phenomenal rise, however, began after the suppression of the so-called Rohm putsch on June 30, 1934, the "Night of the Long Knives." Four days later, Mueller was promoted to SS-Obersturmfuehrer and put in charge of senior officials; by January 30, 1937, he was an SS-Standartenfuehrer. It was only in June of that year, however, that he was given the rank of senior administrative councillor and criminal police councillor. From September 1939 to the end of the war, Mueller was head of Section IV (Gestapo) of the Reichssicherheitshauptamt (Reich Main Security Office; RSHA) and deputy commander of the Security Police and the SD. He was responsible to Heydrich and, after Heydrich's assassination, to his successor, Ernst Kaltenbrunner. Mueller was one of the most powerful men in the Nazi State terror system, but he stayed out of the limelight. On April 20, 1939, he became an SS-Oberfuehrer; and on December 14, 1940, an SS-Brigadefuehrer; two days later, he was also promoted to Generalmajor of the police. On November 9, Mueller was appointed an SS-Gruppenfuehrer and to the equivalent rank in the police.
Loyalty to Hitler
Mueller remained loyal to Adolf Hitler to the end in the bunker where Hitler spent his last weeks. On October 15, 1944, Mueller, the ex-pilot, was awarded the Knight's cross with crossed swords (the highest German award in World War II) for excellence, in recognition of his services in the merciless pursuit of the participants in the July 20, 1944, plot against Hitler. These included some of Mueller's friends, such as Count Wolf Heinrich von Helldorf, Arthur Nebe, Hans Gisevius, and Friedrich Werner von der Schulenburg.
Unknown Fate
All trace of Mueller was lost on April 29, 1945. There exists no confirmation of the rumours that he defected to the Soviet secret service, or that he escaped to the Middle East or Latin America, or that he remained alive.
