One of the Soviet Union's earliest war crimes was the Katyn massacre (Polish: "zbrodnia katyńska", "Katyń crime"; Russian: Катынская резня "Katynskaya reznya", "Katyn massacre", or Russian: Катынский расстрел, "Katyn execution by shooting"), a series of mass executions of Polish military officers and intelligentsia carried out by the Soviet Union, specifically the NKVD ("People's Commissariat for Internal Affairs", aka the Soviet secret police) in April and May 1940. Though the killings took place at several places, the massacre is named after the Katyn Forest, where some of the mass graves were first discovered.