Since 2010 the Essen liaison office of the International Police Association (IPA) has been running the Police-historical Collection consisting of a variety of police-historical exhibits and rarities from imperial times to the present. About 5.000 exhibits, among them Prussian spiked helmets, police uniforms from the Weimar Republic and the 150-piece and therefore largest collection of reward posters, were brought together by Chief Inspector Rainer Wittka and former State Office of Criminal Investigations officer Heinz Zengeler.