Scrambling to meet the "new threat", Gestapo headquarters in Zichenau (Ciechanów) formed a lesser known unit called "Kommando SS Zichenau-Schroettersburg", which departed from the sub-station Schröttersburg (Płock) under the command of "SS-Obersturmführer" Hermann Schaper, with the mission to kill Jews, communists and the NKVD collaborators across the local villages and towns in the Bezirk. On 3 July additional formation of "Schutzpolizei" arrived in Białystok from the General Government. It was led by "SS-Hauptsturmführer" Wolfgang Birkner, veteran of "Einsatzgruppe" IV from the Polish Campaign of 1939. The relief unit, called "Kommando Bialystok", was sent in by "SS-Obersturmbannfuhrer" Eberhard Schöngarth on orders from the Reich Main Security Office (RSHA), due to reports of Soviet guerrilla activity in the area with Jews being of course immediately suspected of helping them out. On 10 July 1941, Schaper's unit was split into smaller "Einsatzkommandos" due to requirements of Operation Barbarossa.