The sources used in that article that mention his Soviet life are this very Youtube video(!), his own writings (sometimes under a pseudonym), a single newspaper

The sources used in that article that mention his Soviet life are this very Youtube video(!), his own writings (sometimes under a pseudonym), a single newspaper obituary with no sources except quotes from people that knew him, or the CIA. I don't find any of that particularly convincing, especially when the topic is "propaganda".