It has to be pointed out that the campaign of blaming the Germans for Katyn was by no means limited to the Soviet Union itself - western media was eager to spread Soviet propaganda:
https://www.nytimes.com/1944/01/27/arch ... n-the.html
SOVIET BLAMES FOE IN KILLING OF POLES; Commission Reports on the Katyn Incident, Finds Plot to Hurt Russian Prestige ALLIED PRESS SEES BODIES Correspondents and Daughter of Ambassador Harriman Visit Scene for Data
SMOLENSK, Russia, Jan. 22 (Delayed) An extraordinary Soviet commission investigating German atrocities reported today that its examinations had definitely established that the Germans had individually shot and killed 11,000 Polish officers and men in near-by Katyn forest during August and September, 1941. Seventeen correspondents, Miss Kathleen Harriman, daughter of the American Ambassador, and John Melbe, acting OWI director. in Moscow, came here to see the mass graves in the snow-covered Katyn forest on the eastern bank of the Dnieper and to hear the evidence of six witnesses as well as a summary of the commission's experts, who rebutted German charges that the Polish prisoners of war had been executed by the Russians in March, 1940.
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Western officials knew it was a lie, but choose to suppress the truth:
https://www.reuters.com/article/world/w ... BRE88A0O0/
WARSAW (Reuters) - Franklin D. Roosevelt and Winston Churchill hushed up evidence the Soviet secret police had killed thousands of Polish men in the Katyn forest in 1940 for fear of alienating World War Two ally Josef Stalin, newly-declassified documents show.
An estimated 22,000 Polish military officers and intellectuals were killed in the massacre at Katyn, in western Russia, many of them trucked in from prison camps, shot in the head from behind, and shoved into mass graves.
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Unsurprisingly, the US government radio mouth piece "Voice of America" was also involved in the campaign:
https://www.coldwarradiomuseum.com/time ... tic-radio/
On May 3, 1943, the Office of War Information (OWI) Director Elmer Davis was heard in Europe in a Voice of America (VOA) radio broadcast supporting the Soviet propaganda description of the Katyn Forest massacre of thousands of Polish military officers in Russian captivity. What Davis said in the VOA broadcast and in the same commentary aired by U.S. domestic radio networks was one of the greatest Soviet lies of the 20th century. Davis later claimed that he did not know the truth, but there was strong evidence to suggest that he did.
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The Western Allies did not limit themselves to repeating Soviet propaganda, they fabricated their own Katyn lies, like here:

- Katyn_NYT.jpg (179.41 KiB) Viewed 108 times