After the outbreak of war between Germany and Poland in September 1939, Canaris visited the front, where he saw the devastation rendered by the German military—seeing Warsaw in flames nearly brought him to tears and it was reported that he exclaimed, "our children's children will have to bear the blame for this". He also witnessed examples of the war crimes committed by the "Einsatzgruppen" of the SS, including the burning of the synagogue in Będzin with 200 Polish Jews inside. Moreover, he received reports from "Abwehr" agents about several incidents of mass murder throughout Poland. Canaris visited Hitler's headquarters train on 12 September 1939, at the time in Province of Silesia, to register his objection to the atrocities. Canaris told chief of the "Oberkommando der Wehrmacht" (OKW, Supreme Command of the Armed Forces) Wilhelm Keitel about the "extensive shootings ... and that the nobility and clergy were to be exterminated" to which Keitel informed him that Hitler had already "decided" the matter. Keitel warned Canaris to go no further with his protest, as the detailed plan of atrocities came directly from Hitler.