Robert Kempner was a successful lawyer in Berlin during the 1920s who then became the chief legal advisor to the Prussian police. Kempner participated in the investigation and prosecution of Adolf Hitler and Wilhelm Frick in 1924, following Hitler's attempt to overthrow the German government in the Beer Hall Putsch. At the time he recommended the dissolution of the Nazi Party.
After the Nazi rise to power in 1933, Hermann Göring fired Kempner from his position because of his anti-Nazi activities. Kempner was then arrested and held for two months in a concentration camp after being accused of leaking information about Germany's rearmament, activities forbidden under the post-World War I Treaty of Versailles. In 1935, Wilhelm Frick, then the Interior Minister, used Kempner's Jewish background to revoke his German citizenship. Kempner was then expelled from Germany. He taught law for a few years in Italy before immigrating to the United States.
After World War II Kempner returned to Germany, the land of his birth, to serve as assistant US chief counsel during the International Military Tribunal at Nuremberg. In a reversal of fortune, Kempner would prosecute two of his former superiors and persecutors—Göring and Frick. More familiar with the German legal system than any other member of the Allied staff, Kempner headed the Defense Rebuttal Section, the team responsible for anticipating the defense strategies of the accused and for preparing cross-examinations.
Kempner also presented the case against his old nemesis Wilhelm Frick. This irony was not lost on the American press. One headline read, “Man He Exiled Presents Case Against Frick.” Kempner also served as counsel at the 1947–1948 trial of the German Foreign Office and is credited with finding the text of the Wannsee Protocol, a critical historical document in the history of the Holocaust. After Nuremberg, Kempner split his time between the United States and Germany where he represented Jewish clients in Nazi restitution cases. He also appeared as an expert witness at the trial of Adolf Eichmann in Jerusalem in 1961. Kempner died in 1993 at the age of 93.