Nazi   Einsatzgruppen   killed the   Jewish population of   Kiev . [155] [156] [157] [158] [159] October 20–21, 1941 Serbia Kragujevac massacre 2,796-5,000 Nazi   soldiers massacred Serb and Roma hostages in retaliation for attacks on the occupying forces. October 22–24, 1941 Odessa ,   Soviet Union Odessa Massacre