The deportees were forced into rail cars, most of which were windowless, unheated cattle cars, and squeezed in so tightly that most were forced to stand. The doors were then sealed shut from the outside. Neither drinking water nor sanitary facilities were available. Each car held more than 120 people, and many froze or suffocated to death or succumbed to disease during the trip to the camps. The dead were not removed from the cars during the journey because the Nazi bureaucracy insisted that each body entering a car be accounted for at the destination.
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.