In 1944, having retaken the Katyn area, the Soviets exhumed the bodies again. That same year, President of the United States Franklin Delano Roosevelt assigned Captain George Earle, his special emissary to the Balkans, to compile information on Katyn. Earle did so, using contacts in Bulgaria and Romania. Earle too concluded that the Soviet Union was guilty. FDR rejected that conclusion, saying that he was convinced of Nazi Germany's responsibility, and ordered Earle's report suppressed. When Earle formally requested permission to publish his findings, the President gave him a written order to desist. Earle was reassigned and spent the rest of the war in American Samoa.
After the WWII the Polish Communist authorities covered up the matter in concord with the Soviet propaganda, deliberately censoring any sources that might shed some light on the Soviet crime. The truth was not publicly known until the fall of communism in 1989.
In 1946, the chief Soviet prosecutor at the Nuremberg Trials tried to indict Germany for the Katyn killings, stating that "one of the most important criminal acts for which the major war criminals are responsible was the mass execution of Polish prisoners of war shot in the Katyn forest near Smolensk by the German fascist invaders," but dropped the matter after the United States and the United Kingdom refused to support it and German lawyers mounted an embarrassing defense. Katyn is not mentioned in any of the Nuremberg judgements.
The question of responsibility remained controversial in the West as well as behind the Iron Curtain. For example, in the United Kingdom in the late 1970s, plans for a memorial to the victims bearing the date 1940 (rather 1941) were condemned as provocative in the political climate of the Cold War.
In 1989 Soviet scholars revealed that Joseph Stalin had indeed ordered the massacre, and in 1990 Mikhail Gorbachev admitted that the Narodny Kommisariat Vnutrennikh Del (NKVD) had executed the Poles, confirmed two other burial sites similar to the site at Katyn. In 1992, with the collapse of the Soviet Union, Russian officials released the order, signed by Joseph Stalin and dated March 1940, to execute by shooting some 25,700 Poles.
The corrupt investigations that wrongly indicted the German State rather than the Soviet State for the killings are sometimes used to impeach the Nuremberg Trials in their entirety, often in support of Holocaust denial, or to question the legitimacy and/or wisdom of using the criminal law to prohibit Holocaust denial.
See also: Józef Mackiewicz