At around this time , after several Gestapo – NKVD Conferences , Soviet NKVD officers also conducted lengthy interrogations of 300,000 Polish POWs in camps that were , in effect , a selection process to determine who would be killed . On March 5 , 1940 , in what would later be known as the Katyn massacre , where 22,000 military and intellectuals were executed they were labeled " nationalists and counterrevolutionaries " , kept at camps and prisons in western Ukraine and Belarus
Katyn massacre
Katyn massacre
Molotov–Ribbentrop Pact