The RSHA oversaw the "Einsatzgruppen", death squads that were formed under the direction of Heydrich and operated by the SS. Originally part of the SiPo, in September 1939 the operational control of the "Einsatzgruppen" was taken over by the RSHA. When the units were re-formed prior to the invasion of the Soviet Union in 1941, the men of the "Einsatzgruppen" were recruited from the SD, Gestapo, Kripo, Orpo, and Waffen-SS. The units followed the invasion forces of the German Army into Eastern Europe. In its role as the national and NSDAP security service, the RSHA coordinated activities among a number of different agencies that had wide-ranging responsibilities within the Reich. Not infrequently, commanders of "Einsatzgruppen" and "Einsatzkommando" sub-units were also desk officers from the main office of the RSHA. Historian Raul Hilberg estimates that between 1941 and 1945 the "Einsatzgruppen", related agencies, and foreign auxiliary troops co-opted by the Nazis, killed more than two million people, including 1.3 million Jews.