The Katyn massacre was a mass murder of thousands of Polish prisoners of war (primarily military officers), intellectuals, policemen, and other public servants by the Soviet NKVD. After 3 April, 1940, at least 22,436 POWs and prisoners were executed: 15,131 POWs (most or all of them from the three camps) and at least 7,305 prisoners in western parts of Belarus and Ukraine.