This volume is a continuation of the collection "Katyn. Prisoners of undeclared war." It includes archival materials from the funds of I.V. Stalin, the Central Committee of the All-Union Communist Party of Bolsheviks and its Politburo, NKVD, NKID, etc. They reveal the history of the preparation, conduct and consequences of the execution of about 22 thousand Polish prisoners of war, officers, police officers and prisoners of prisons, carried out by decision of the Politburo of the Central Committee of the All-Union Communist Party of Bolsheviks in April-May 1940.