The author is an Austrian-British investigative journalist and biographer best known for her extensive interviews with Mary Bell, an adolescent who killed two children, and Franz Stangl. She fled to France when she was 17 after Germany annexed Austria. There, she worked with orphans during the German occupation until she fled the country because of her connection to the French Resistance. After the war, she worked with the United Nations to reunite children kidnapped by Nazi Germany with their families.

Sereny’s shared Austrian nationality with Stangl is crucial to her book. Not only did she speak German, allowing her to develop a greater rapport with Stangl than if she needed an interpreter, but she identified his telling habit of reverting to the Austrian vernacular of his childhood when answering difficult questions. Because she grew up in Austria like Stangl, she could compare his childhood experiences with her own. For example, when Stangl explains that he joined the police during the Great Depression because he saw security in a uniformed job, Sereny remembers also feeling that there was security in a uniform.

As the book’s subtitle indicates, Sereny's goal in interviewing Stangl is to plumb the depths of his conscience and understand how he could oversee the murders of 1.