The first mass killing of 3,000 Jews by the German police occurred in Białystok on 12 July 1941 in the territories of Poland annexed by the Soviet Union,[10] followed by the Bloody Sunday massacre of 10,000-12,000 Jews by the Reserve Police Battalion 133, perpetrated in Stanisławów (now Ivano-Frankivsk, Ukraine) on 12 October 1941 with the aid of SiPo and the Ukrainian Auxiliary Police.[11][12][13]