Moreover, some of the cruelest experiments conducted in Auschwitz, on mass sterilization and the effects of starvation, were carried out by other camp physicians. Mengele was one of many among a whole corps of medical staff — doctors, pharmacists, nurses, orderlies — posted in the camp. Apart from the experiments, their duties consisted of what “ordinary doctors” regularly and legitimately do. These included responsibility for the health of SS members and camp inmates, and preventing the spread of disease (like typhus, one of Mengele’s achievements). This was the larger context in which Mengele worked, enabling him to enthusiastically exercise his — albeit racially perverted and ideologically inflected — scientific and research interests. With its vast available human resources, Auschwitz became an ideal laboratory.

“No one in history,” Marwell writes, “had had access to the raw material that stood before him or had been so liberated from the restraints that tamed ambition and limited scientific progress.” It was here that the line between being an ordinary “Hippocratic” doctor and a mass murderer was crossed. For physicians at Auschwitz, the informing biomedical Nazi vision that combined combating and destroying enemies of the Aryan race (above all, Jews), with positive steps to preserve and improve the German racial community, seamlessly encouraged the corruption of medical ethics, the denial of basic humanity and the practice of ruthless experimentation and medicalized killings. What particularly distinguished Mengele from other physicians was that he reveled in the culture that had been created in Auschwitz, in the opportunities and power it gave him. He saw himself as engaged in a putatively “cutting edge” scientific endeavor. He was quite correct when, in a remarkable letter to his son, he declared that he had not invented Auschwitz, it already existed. But it was in its unparalleled enabling culture that Mengele “realized” himself and, as the psychiatrist Robert Jay Lifton put it, “his actions so well articulated the camp’s essence.”

Throughout the postwar years he expressed no remorse and either remained oblivious to, or rationalized, the enormity of his crimes. He remained a convinced Nazi and when pushed, he resorted to the timeworn justification that he had to do his duty and carry out orders. He had never harmed anyone personally. In any case, as Rolf summarized his father’s words: “He couldn’t help anyone. On the platform for instance. What was he to do, when the half-dead and infected people arrived? … His job was to clarify only: ‘able to work’ and ‘unable to work.’ … He thinks he saved the lives of thousands of people in that way. He hasn’t ordered the extermination and he is not responsible. Also, the twins owe their lives to him.”

What specifically distinguishes Marwell’s account from previous studies concerns his personal involvement in the Justice Department’s Office of Special Investigations (O.S.I.) and the search for and identification of Mengele. Much of the volume is taken up with Mengele’s escape to, and life in, various South American countries and the bungled attempts to locate and capture him. Astonishingly, Mengele was in American captivity in 1945 and the Israelis found him in 1960; for different reasons both ventures were simply dropped. Marwell comprehensively recounts this case of justice denied, and how — helped by his wealthy family, loyal friends and Nazi sympathizers — Mengele succeeded in evading his would-be captors. There is also highly detailed reportage regarding the seemingly endless investigations and multiple conflicts surrounding the interpretation of the medical and forensic evidence that in 1992 definitively established that Mengele had died in Brazil in 1979.

“Finally, in the end,” Marwell writes with a certain flourish, “I held his bones in my hands.” When in October 1992 the O.S.I. submitted its concluding report, “In the Matter of Josef Mengele,” it was to the assistant attorney general for the criminal division, Robert S. Mueller III. He later handed it to his boss, the attorney general, William P. Barr.