Claim: American psychologist Gustave Mark Gilbert served as prison psychologist of World War II German prisoners and participated in the Nuremberg trials attesting to the sanity of Rudolf Hess.
Evidence: Gustave Mark Gilbert (September 30, 1911 – February 6, 1977) was an American psychologist best known for his writings containing observations of high-ranking Nazi leaders during the Nuremberg trials. Gilbert was appointed the prison psychologist of the German prisoners. In 1945, after the end of the war, Gilbert was sent to Nuremberg, Germany, as a translator for the International Military Tribunal for the trials of the World War II German prisoners. During the process of the trials Gilbert became, after Douglas Kelley, the confidant of Hermann Göring, Joachim von Ribbentrop, Wilhelm Keitel, Hans Frank, Oswald Pohl, Otto Ohlendorf, Rudolf Höss, and Ernst Kaltenbrunner, among others. Gilbert also participated in the Nuremberg trials as the American Military Chief Psychologist and provided testimony attesting to the sanity of Rudolf Hess.