The German view of the Roma as hereditary criminals and "asocials" was reflected in their classification in the concentration camps, where they were usually counted among the asocials and given black triangles to wear.[420] According to Niewyk and Nicosia, at least 130,000 died out of nearly one million in German-occupied Europe.[415] The United States Holocaust Memorial Museum calculates at least 220,000.[421] Ian Hancock, who specializes in Romani history and culture, argues for between 500,000 and 1,500,000.[422] The treatment of the Roma was not consistent across German-occupied territories. Those in France and the Low Countries were subject to restrictions on movement and some confinement to collection camps, while those in Central and Eastern Europe were sent to concentration camps and murdered by soldiers and execution squads.[423] Before being sent to the camps, the Roma were herded into ghettos, including several hundred into the Warsaw Ghetto.[219] Further east, teams of Einsatzgruppen tracked down Romani encampments and murdered the inhabitants on the spot, leaving no records of the victims.[423] After the Germans occupied Hungary, 1,000 Roma were deported to Auschwitz.[424][x]
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]