The mass murder of Jews began in the summer of 1941. By that time, conditions in the Ghettos in Poland were abysmal. The Nazi's were purposely starving the Jews to death in all of the major ghettos. Thousands a month were already dying in Warsaw alone. Hitler made the decision to kill the Jews in 1939. He stated it publicly many times. In January 1939 he said, "Today I will once more be a prophet: if the international Jewish financiers in and outside Europe should succeed in plunging the nations once more into a world war, then the result will not be the Bolshevizing of the earth, and thus the victory of Jewry, but the annihilation of the Jewish race in Europe!"
The mass murder of Jews began when Adolph Hitler opened his mouth and the German people shut theirs.