Journalist Gitta Sereny’s 1974 biography of Franz Stangl, the head of the Nazi extermination camp Treblinka in German-occupied Poland, is titled ‘Into That Darkness’ An Examination of Conscience. Stangl was found guilty of killing 900,000 people. Based on seventy hours of interviews with Stangl, the book offers an insight into the mind of a man who was always trying to justify his part in Hitler’s ultimate solution.