On August 4, 1944, the Gestapo (German Secret State Police) discovered the hiding place. It has been long thought that the authorities acted after being tipped off by an anonymous Dutch caller. But a more recent theory is that the German SD discovered the hiding place by chance, while investigating reports that illegal work and fraud with ration coupons were occurring at the house.
Nazi Germany maintained concentration camps (German: Konzentrationslager, KZ or KL) throughout the territories it controlled before and during the Second World War. The first Nazi camps were erected in Germany in March 1933 immediately after Hitler became Chancellor and his Nazi Party was given control of the police by Reich Interior Minister Wilhelm Frick and Prussian Acting Interior Minister Hermann Göring. Used to hold and torture political opponents and union organizers, the camps initially held around 45,000 prisoners. In 1933–1939, before the onset of war, most prisoners consisted of German Communists, Socialists, Social Democrats, Roma, Jehovah's Witnesses, homosexuals, and persons accused of 'asocial' or socially 'deviant' behavior by the Germans.