Sobibor survivor Thomas Blatt was among those called to testify as a witness against Frenzel at the post-war trial, and when Blatt traveled to the court venue city, Blatt and Frenzel met at a hotel in order to discuss historical questions and technical details about camp operation for the history of the uprising Blatt was then writing; the event is presumed to be the only time that a Nazi death camp supervisor was interviewed by a death camp prisoner. In the years after the war, Frenzel frequently expressed remorse for his actions, but explained that he had simply complied with his duty. He renounced his belief in the Nazi Party.