After obtaining a copy of his birth certificate through the West German embassy in 1956, Mengele was issued with an Argentine foreign residence permit under his real name. He used this document to obtain a West German passport, also using his real name, and embarked on a trip to Europe. He met up with his son Rolf (who was told Mengele was his "Uncle Fritz") and his widowed sister-in-law Martha, for a ski holiday in Switzerland; he also spent a week in his home town of Günzburg. When he returned to Argentina in September 1956, Mengele began living under his real name. Martha and her son Karl Heinz followed about a month later, and the three began living together. Josef and Martha were married in 1958 while on holiday in Uruguay, and they bought a house in Buenos Aires. Mengele's business interests now included part ownership of Fadro Farm, a pharmaceutical company. Along with several other doctors, Mengele was questioned in 1958 on suspicion of practicing medicine without a license when a teenage girl died after an abortion, but he was released without charge. Aware that the publicity would 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". He returned to Buenos Aires several times to settle his business affairs and visit his family. Martha and Karl lived in a boarding house in the city until December 1960, when they returned to Germany.
Mengele sailed to Argentina in July 1949, assisted by a network of former SS members. He initially lived in and around Buenos Aires, then fled to Paraguay in 1959 and Brazil in 1960, while being sought by West Germany, Israel, and Nazi hunters such as Simon Wiesenthal who wanted to bring him to trial. He eluded capture in spite of extradition requests by the West German government and clandestine operations by the Israeli intelligence agency Mossad. He drowned in 1979 after suffering a stroke while swimming off the Brazilian coast, and was buried under a false name. His remains were disinterred and positively identified by forensic examination in 1985.