Somewhere within the time of the German declaration of war on the United States in December 1941, Hitler had decided that the Jews of Europe were to be exterminated. Heydrich had issued a plan for the Jews, those being able to work would be worked to death, those that had been unable to work would be killed on the spot. Heydrich had presented this at a meeting and had calculated the number of Jews to be killed at 11 million, and told the attendees that Hitler had placed Himmler in charge of this plan that had been presented. At the concentration camps initially victims were killed by gas van or by firing squads. Until August 1941 when Himmler had attended a shooting of a 100 Jews, nauseated and shaken by the experience, he had become concerned for the SS men mental health. He then decided that alternate methods of killings should be implemented. On his orders, spring of 1942 the camp at Auschwitz had been greatly expanded, with the addition of gas chamber, something like the gas vans, but was a huge room that had been sealed completely. Stuffing these chambers full of people, and through little holes at the top, SS soldiers with gas masks had a can of Zyklon B which was an extremely poisoning gas, had dropped these can and some people had died instantly but others suffered for more then 20 minutes. Himmler had been the main architect of the Holocaust alone, using his deep beliefs in the racist Nazi ideas to justify the mass murdering of millions of victims.