I always thought that the reason the Soviets didn’t get nailed for their crimes is - unlike the Nazis - they didn’t photograph their atrocities.
I realize that some photos exist but where are the newsreels and film footage showing the horrors of the 1930s? I think Stalin was too sly for that.
Seriously ... God only knows what's lurking in the KGB/GRU archives. But no conquering army marched through Moscow to find out. No conquering army marched through the gulags to free the inmates. History is written by the winners. The communist bloody-handed murderers were among the winners. The national socialist bloody-handed murderers were among the losers. The winners uncovered all the losers' dirty laundry, while hiding their own.
How long did it take for them to admit to the Katyn Forest Massacre?