In the spring of 1940, Soviet troops shot approximately 22,000+ Polish officers in the back of the head and buried them in layers. From a mass grave in the Katyn Forest, Nazi German soldiers exhumed the bodies of approximately 4,500 more Polish officers in the spring of 1943.

　　In the spring of 1943, Nazi German soldiers exhumed approximately 4,500 more Polish corpses from a mass grave in the Katyn Forest, where Soviet troops had killed approximately 22,000 more Polish officers in the spring of 1940. Most were Polish army officers deported to concentration camps in the spring of 1940, shot in the back of the head and buried in layers. Poland was a plain without natural fortifications, and the Katyn Forest was located in the Smolensk region of Russia; after March 1940, some 20,000 Polish officers went missing. The rest were executed in Kiev, Kharkov, Kherson (Ukraine), Minsk (Belarus), and Kalinin (now Tveri) prisons. About 180,000 Polish generals were captured by the Soviets, who had signed a non-aggression pact with Germany. Stalin immediately fired back at the Gestapo for the war crimes Germany had uncovered.

　 The Germans found thousands of dead Polish officers in the Katyn forest in the spring of 1943. The corpses had been shot with 9mm caliber pistols. Many of the Poles were reserve officers, doctors, lawyers, teachers, and other intellectuals. About 8,000 officers were missing, and about 4,500 or so bodies were found in the Katyn Forest, some still undiscovered, in the Ribbentrop-Molotov Pact of August 23, 1939, which sealed the alliance between Nazi Germany and the Soviets, and agreed to the partition of Poland, among other things. Only a week later, on September 1, the Germans began their invasion of Poland from the west, and 17 days later it was the Soviets' turn to invade from the east.

　　The U.S. Special Investigative Commission ruled that the Soviets were responsible. With the collapse of Russian communism, the Soviets finally admitted responsibility for the war crimes of the 1990 massacre, admitting that it was NKVD (Soviet secret police) agents under direct orders from Stalin who executed the Polish prisoners in the spring of 1940. Prime Minister Vladimir Putin's initiative, electronic copies of secret documents concerning the Katyn Forest were released on the Internet. There is a note from the executioner, Lavrench Velia, the director of the NKVD, to Stalin. He proposed the summary execution of the Poles, which Stalin approved with a blue pencil. The communists, however, refused to recognize the authenticity of the document in the archives, claiming that it was a forgery by Goebbels and others in Nazi Germany.