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.

He initially lived in and around Buenos Aires, but fled to Paraguay in 1959 and later Brazil in 1960, all while being sought by West Germany, Israel, and Nazi hunters such as Simon Wiesenthal, who wanted to bring him to trial.

Mengele eluded capture in spite of extradition requests by the West German government and clandestine operations by the Israeli intelligence agency Mossad.

[9] In January 1937, he joined the Institute for Hereditary Biology and Racial Hygiene in Frankfurt, where he worked for Otmar Freiherr von Verschuer, a German geneticist with a particular interest in researching twins.

)[15] In a letter of recommendation, Von Verschuer praised Mengele's reliability and his ability to verbally present complex material in a clear manner.

[18] The ideology of Nazism brought together elements of antisemitism, racial hygiene, and eugenics, and combined them with pan-Germanism and territorial expansionism with the goal of obtaining more Lebensraum ("living space") for the Germanic people.

He received basic training in 1938 with the Gebirgsjäger (mountain light infantry) and was called up for service in the Wehrmacht (Nazi armed forces) in June 1940, some months after the outbreak of World War II.

Following his recovery, he was transferred to the headquarters of the SS Race and Settlement Main Office in Berlin, at which point he resumed his association with Von Verschuer, who had become director of the Kaiser Wilhelm Institute of Anthropology, Human Heredity, and Eugenics.

[28] By July 1942, SS doctors were conducting selections where incoming Jews were segregated, and those considered able to work were admitted into the camp while those deemed unfit for labor were immediately murdered in the gas chambers.

[35] Mengele's work also involved carrying out selections, a task that he chose to perform even when he was not assigned to do so, in the hope of finding subjects for his experiments,[36] with a particular interest in locating sets of twins.

[37] In contrast to most of the other SS doctors, who viewed selections as one of their most stressful and unpleasant duties, he undertook the task with a flamboyant air, often smiling or whistling.

The patients were isolated in separate barracks and several afflicted children were killed so that their preserved heads and organs could be sent to the SS Medical Academy in Graz and other facilities for study.

[43] A grant was later provided by the Deutsche Forschungsgemeinschaft ('German Research Foundation'), at the request of Von Verschuer, who received regular reports and shipments of specimens from Mengele.

[60] In his 1986 book, Lifton described Mengele as sadistic, lacking empathy, and extremely antisemitic, believing the Jews should be eliminated as an inferior and dangerous race.

[66] After several months on the run, including a trip back to the Soviet-occupied area to recover his Auschwitz records, Mengele found work near Rosenheim as a farmhand.

Assisted by a network of former SS members, he used the ratline to travel to Genoa, where he obtained a passport from the International Committee of the Red Cross under the alias "Helmut Gregor", and sailed to Argentina in July 1949.

He next worked as a salesman for his family's farm equipment company, Karl Mengele & Sons, and in 1951 he began making frequent trips to Paraguay as a regional sales representative.

[74] He moved into an apartment in central Buenos Aires in 1953, used family funds to buy a part interest in a carpentry concern, and then rented a house in the suburb of Olivos in 1954.

[77][78] He met with his son Rolf (who was told Mengele was his "Uncle Fritz")[79] and his widowed sister-in-law Martha, for a ski holiday in Switzerland; he also spent a week in his home town of Günzburg.

Aware that the publicity could lead to his Nazi background and wartime activities being discovered, he took an extended business trip to Paraguay and was granted citizenship there in 1959 under the name "José Mengele".

[86] Working in West Germany, Nazi hunters Simon Wiesenthal and Hermann Langbein collected information from witnesses about Mengele's wartime activities.

[92] In May 1960, Isser Harel, director of the Israeli intelligence agency Mossad, personally led the successful effort to capture Adolf Eichmann in Buenos Aires.

[94] Despite having provided Mengele with legal documents using his real name in 1956 (which had enabled him to formalize his permanent residency in Argentina), West Germany was now offering a reward for his capture.

Former pilot Hans-Ulrich Rudel put him in touch with the Nazi supporter Wolfgang Gerhard, who helped Mengele cross the border into Brazil.

[100] This potential breakthrough was reported to Harel, but the logistics of staging a capture, the budgetary constraints of the search operation, and the priority of focusing on Israel's deteriorating relationship with Egypt led the Mossad chief to call off the manhunt in 1962.

[103] When Wolfgang Gerhard returned to Germany in 1971 to seek medical treatment for his ailing wife and son, he gave his identity card to Mengele.

[107] Rolf, who had not seen his father since the ski holiday in 1956, visited him at the bungalow in 1977; he found an "unrepentant Nazi" who claimed he had never personally harmed anyone and only carried out his duties as an officer.

[119] Worldwide interest in the case was heightened by a mock trial held in Jerusalem in February 1985, featuring the testimonies of over one hundred victims of Mengele's experiments.

[120] On 31 May 1985, acting on intelligence received by the West German prosecutor's office, police raided the house of Hans Sedlmeier, a lifelong friend of Mengele and sales manager of the family firm in Günzburg.

[125] In 1992, DNA testing confirmed Mengele's identity beyond doubt,[126] but family members refused repeated requests by Brazilian officials to repatriate the remains to Germany.