 Researches in the Stasi records showed that Gerstner had been registered with the ministry as an informer since 1975.He had been identified in Stasi files under the code name "IM Ritter", a characteristically ironic choice of name, since apart from "Ritter" being the German word for "knight", Gerstner's biological father had been the Nazi diplomat Karl Ritter.The Stasi had paid Gerstner a supplementary salary amounting to 2,000 marks per month for his information.