Katyn Massacre
The Katyń Massacre was the mass execution during World War II of several thousand Polish Army and Police Officers who had surrendered to the Soviet Union during the annexation of Poland as required by the terms of the Molotov-Ribbentrop Pact. They were placed in internment camps near Katyń, where they remained until 1941, wherein the German advance took over the territory. While Western media and historiography commonly claim that the NKVD executed the Poles in 1940, before the Germans took over, this does not have any factual basis, with the majority of "evidence" being a repetition of Nazi-tampered "proof".
Anti-Soviet accusation
What is presented are a bunch of dead officers with German bullets in the back of the skull or otherwise executed. The "official" version is that the Soviets somehow foresaw that the Germans will attack them in the future, despite them currently having a non-aggression pact with Germany and Soviet High Command not knowing whether the Germans would decide to attack that year or 4 years from then. On top of this there was also was economic cooperation, so that they would use German bullets - despite never using German weapons in any capacity - because they somehow knew that years into the future some investigation would find the bodies and blame the defeated Germans for this if they discovered it. Moreover, somehow the NKVD would know the fact that the Germans consistently massacred captured Slavic POWs and civilians on the Eastern Front and used a specific mass-grave system to do so, and replicated it, but only burying them in shallow enough graves as to let the Germans find them and out them first. The sheer inanity of such a conspiracy does not hold up to scrutiny, yet that is the scenario presented.
The Nazi "proof"
Debunking false evidence
Evidence of Nazi involvement
Legal assertions
During the Perestroika and the 1990s among the major demonstrative actions were calls for the Communist Party to be put on trial for various perceived crimes against the people. Among the issues brought up was Katyń, however the accusations and the evidence did not hold up in court and even current Courts in Russia and the European Union have not found conclusive evidence, despite anti-communist sentiments in both.
Ethical and socio-economic debate
Even if one was to believe the claim that the NKVD did in fact execute the Polish POWs in 1940 as claimed, the question is of the morality and actual social impact outside of propaganda.
“Millions of Poles were killed in German death camps throughout the war, and with considerably less sustained outcry from the London government. Indeed, only that very month the Germans were annihilating some 50000 Jews in the Warsaw Ghetto rebellion, and far less was heard from London on this matter. Katyń was an infinitely more sensitive issue because the men killed there, as Polish underground leader Tadeusz Bor-Komorowski described them, 'had been the elite of the Polish nation . . .,' that is to say, the friends and family of the exiles in London. Whoever destroyed the officers at Katyń had taken a step towards implementing a social revolution in Poland, and on the basis of class solidarity, the London Poles felt one officer was worth many Jews or peasants.” - Gabriel Kolko, The Politics of War: The World and United States Foreign Policy, 1943–1945. (1968) p. 105.