Nazi Germany, June 1943, Buchenwald concentration camp. The last place you'd expect to find any form of justice. And yet justice against the SS men who brutalised the prisoners here would be attempted by the unlikeliest of sources – SS officer Konrad Morgen.

Nazi Germany, despite the atrocities it carried out on an industrial scale, still had legislation and a legal system, and Morgen used these laws to bring individual members of the SS to justice for their crimes. He was a fearless investigating judge and police official, and when he crossed swords with more powerful forces inside the SS, he was demoted and sent by Heinrich Himmler himself to the Eastern Front as an ordinary soldier in the Waffen SS.

But Morgen's skills were still required and he returned to launch a series of criminal investigations in various concentration camps, including Buchenwald. As a direct result of his work, two concentration camp commandants were shot before the end of the war and he arrested three others. Targets of his investigations included Adolf Eichmann, one of the architects of the Holocaust, and Rudolf Höss, the infamous commandant of Auschwitz.

Described by historian John Toland as 'the man who did the most to hinder the atrocities in the East', Konrad Morgen pursued Nazi Germany's worst murderers from inside the SS. This is his incredible true story.