It started with a hunch. When Philippe Sands was researching his 2020 bestseller The Ratline he came across a letter held in the dusty family archive of a crumbling schloss in Austria. It was addressed to Otto von Wächter, the SS officer who was the subject of his book, written to him by a former colleague who had escaped postwar Europe and justice to Syria. “And I just wondered, who is this character writing from Damascus?” remembers Sands, speaking on a video call from his home in London. So he looked up this Walther Rauff to discover he was the...