Once the Nazis took over Budapest in 1944 and began deporting Jews to the death camps, Lutz negotiated a special deal with the Hungarian government and the Nazis: he had permission to issue protective letters to 8,000 Hungarian Jews for emigration to Palestine. Lutz then deliberately misinterpreted his permission for 8,000 as applying to families rather than individuals, and proceeded to issue tens of thousands of additional protective letters, all of them bearing a number between one and 8,000. He also set up some 76 safe houses around Budapest, declaring them annexes of the Swiss legation. Among the safe houses was the now well-known "Glass House" (Üvegház) at Vadász Street 29. About 3,000 Jews found refuge at the Glass House and in a neighboring building.
Meanwhile, Zvi Aharoni, one of the Mossad agents who had been involved in the Eichmann capture, was placed in charge of a team of agents tasked with tracking down Mengele and bringing him to trial in Israel. Their inquiries in Paraguay revealed no clues to his whereabouts, and they were unable to intercept any correspondence between Mengele and his wife Martha, who was then living in Italy. Agents that were following Rudel's movements also failed to produce any leads. Aharoni and his team followed Gerhard to a rural area near São Paulo, where they identified a European man whom they believed to be Mengele. 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 hunt for Mengele in 1962.
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.