The Order Police battalions, operating both independently and in conjunction with the Einsatzgruppen, became an integral part of the Final Solution in the two years following the attack on the Soviet Union on 22 June 1941, Operation Barbarossa. The first mass-murder of 3,000 Jews by Police Battalion 309 occurred in occupied Białystok on 12 July 1941.Browning 1998, pp. 9-12 (26/298 in PDF). Police battalions were part of the first and second wave of murders in 1941–42 in the territories of Poland annexed by the Soviet Union and also during the killing operations within the 1939 borders of the USSR, whether as part of Order Police regiments, or as separate units reporting directly to the local SS and Police Leaders.Hillberg, pp. 175, 192–198, en passim. They included the Reserve Police Battalion 101 from Hamburg, Battalion 133 of the Nürnberg Order Police, Police Battalions 45, 309 from Koln, and 316 from Bottrop-Oberhausen. Their murder operations bore the brunt of the Holocaust by bullet on the Eastern Front. In the immediate aftermath of World War II, this latter role was obscured both by the lack of court evidence and by deliberate obfuscation, while most of the focus was on the better-known Einsatzgruppen ("Operational groups") who reported to the Reichssicherheitshauptamt (RSHA) under Reinhard Heydrich.Hillberg, Raul, The Destruction of the European Jews, Holmes & Meir: NY, NY, 1985, pp. 100–106.
