Eugene, a Belgian computer programmer, has retired to a cottage in southern Paraguay, and the pride of his golden years is his view. From his stone patio, he sees forested hills, the fringes of yerba mate plantations, and, in the distance, the crumbling ruins of a Jesuit settlement two centuries old. “Like a picture,” he says, and I nod to agree, even though my mind is not on the beautiful vista, but on the dark figure who once shared it.

The Nazi doctor Josef Mengele cheated justice for decades by hiding out in South America, sometimes in these very hills. Had he stayed in Germany he would almost certainly have died by the noose. Jews and Gypsies at Auschwitz called him “the Angel of Death”: He killed men and women for the dubious medical value of dissecting them, and for pleasure. He injected dyes into children’s eyes to see if… More…