Nebe rose through the ranks of the Berlin and Prussian police forces to become head of Nazi Germany's Criminal Police (Kriminalpolizei; Kripo) in 1936, which was folded into the Reich Main Security Office (RSHA) in 1939. Prior to the 1941 German invasion of the Soviet Union, Nebe volunteered to serve as commanding officer of Einsatzgruppe B. The killing unit was deployed in the Army Group Centre Rear Area, in modern-day Belarus, and reported over 45,000 victims by November 1941. In late 1941, Nebe was posted back to Berlin and resumed his career within the RSHA.