Owing to his political resistance activities against the French occupation of the Ruhr, Best was arrested and briefly imprisoned. In 1930, he joined the Nazi Party (NSDAP) and by 1931—before the Nazis assumed power—he was already a member of the SS. Sometime in 1931, he was forced out of judicial service in the German federal state of Hesse following the discovery of the Boxheim Documents, which were blueprints for a Nazi putsch he had written.