Now, Katyn massacre happened in 1940, but this 'trial-and-court' thingy and declaring it as a war crime is a post USSR issue.
"Unfortunately we have had to give up Katyn. The Bolsheviks undoubtedly will soon 'find' that we shot 12,000 Polish officers. That episode is one that is going to cause us quite a little trouble in the future. The Soviets are undoubtedly going to make it their business to discover as many mass graves as possible and then blame it on us." - Josef Göbbels
In private, Churchill agreed that the atrocity was likely carried out by the Soviets. According to Edward Raczyński, Churchill admitted on 15 April 1943 during a conversation with General Sikorski: "Alas, the German revelations are probably true. The Bolsheviks can be very cruel."[56] However, at the same time, on 24 April 1943 Churchill assured the Soviets: "We shall certainly oppose vigorously any 'investigation' by the International Red Cross or any other body in any territory under German authority. Such investigation would be a fraud and its conclusions reached by terrorism."[57] Unofficial or classified UK documents concluded that Soviet guilt was a "near certainty", but the alliance with the Soviets was deemed to be more important than moral issues; thus the official version supported the Soviets, up to censoring any contradictory accounts.
From 28 December 1945 to 4 January 1946, seven servicemen of the German Wehrmacht were tried by a Soviet military court in Leningrad. One of them, Arno Diere, was charged with helping to dig the Katyn graves during the execution. Diere, who was accused of murder using machine-guns in Soviet villages, confessed to having taken part in burial (though not the execution) of 15–20 thousand Polish POWs in Katyn. For this he was spared execution and was given 15 years of hard labor. His confession was full of absurdities, and thus he was not used as a Soviet prosecution witness during the Nuremberg trials. In a note of 29 November 1954 he recanted his confession, claiming that he was forced to confess by the investigators.[64]
At the London conference that drew up the indictments of German war crimes before the Nuremberg trials, the Soviet negotiators put forward the allegation, "In September 1941, 925 Polish officers who were prisoners of war were killed in the Katyn Forest near Smolensk." The U.S. negotiators agreed to include it, but were "embarrassed" by the inclusion (noting that the allegation had been debated extensively in the press) and concluded that it would be up to the Soviets to sustain it.[65] At the trials in 1946, Soviet General Roman Rudenko, raised the indictment, 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,"[66] but failed to make the case and the U.S. and British judges dismissed the charges.[67] It was not the purpose of the court to determine whether Germany or the Soviet Union was responsible for the crime, but rather to attribute the crime to at least one of the defendants, which the court was unable to do.[68]
Katyn massacre - Wikipedia, the free encyclopedia