We can be sure because the documentary evidence recovered from Soviet archives is corroborated by the documentary evidence gathered by Western law enforcement agencies and by the inconsistencies in Demjanjuk's own account of his wartime whereabouts.
Our government spent a moderate amount of money to prove that a man who fraudulently entered our country was in fact a war criminal. And, guess what? It turns out that he was actually a war criminal.
I guess the Communists knew there would be a lot of war criminals from the Ukraine and so they executed ten million or so of them in advance. Who could have a problem with that?
I thought we were sure, SURE, that he was Ivan the Terrible.