Why do men commit evil? Were the kommandants who ran the Nazi death camps psychopaths? Did they have subnormal intelligence? Were they just ordinary men who made appalling decisions?

I have been thinking about these questions ever since I found out that my great-uncle, Hanns Alexander, a German Jew, was a Nazi Hunter. At the end of the Second World War he tracked down and caught one of the worst mass murderers of all time, Rudolf Höss, the Kommandant of Auschwitz.

These were also the questions that a team of American psychologists and psychiatrists were directed to answer during the Nuremberg Trials that opened on November 20, 1945, six months after the war’s end.