In 1941, German forces occupied much of the Kingdom. Nazi secret police, Gestapo , took over the fairgrounds ( Sajmište ). They encircled it with several rings of barbed wire turning it into a "collection centre". It eventually became an extermination camp . Until May 1942 it was mostly used to kill off Jews from Belgrade and other parts of Serbia, and from April 1942 onwards, it also held political prisoners. Executions of captured prisoners lasted as long as the camp existed. November 1946 report released by the Yugoslav State Commission for Crimes of Occupiers and their Collaborators claims that close to 100,000 prisoners came through the Sajmište's gates. It is estimated that around 48,000 people perished inside the camp.