It is estimated that by 1942 Einsatzgruppen had killed more than 1 million Soviet troops. These victims were either shot or gassed. Jews were not the only ones killed. People who opposed Hitler were also murdered. 20th century techniques of mass production were applied in the Final Solution. Engineers of the Final Solution used these ways to cheaply and efficiently murder millions of Jews there were many ways the Nazis murdered people. Some ways were crematoriums, electrocution, injections, flame throwers, hand grenades, and gas chambers. Units of the S.S. that were specially trained followed German troops called the first wave. These squads made up the Einsatzgruppen. Nazis genocide was targeted towards Jews mass murder was targeted towards other Non-Aryans.      
The first killing center set up in occupied Polish lands was the camp at Chełmno on the Ner; Jews brought in from the ghettos in the Wartheland were being killed there from December 1941. Three more camps, somewhat larger, were opened at Bełżec, Sobibor, and Treblinka (in what was known as “Aktion Reinhard”) somewhat later, between March and July 1942.
Before the war, Mengele had received doctorates in anthropology and medicine, and began a career as a researcher. He joined the Nazi Party in 1937 and the SS in 1938. He was assigned as a battalion medical officer at the start of World War II, then transferred to the Nazi concentration camps service in early 1943 and assigned to Auschwitz, where he saw the opportunity to conduct genetic research on human subjects. His subsequent experiments focused primarily on twins, with little regard for the health or safety of the victims.[2][3]