My degree is in the downfall if the USSR. I have spent a lot of time reading accounts of prisoners. Many never knew because they were not present at their trial.
He has the numbers tattooed on his arm. I know people who knew him in Belarus that I knew separate of him who talked about it.
There were prominent Jews in the politburo. There was also a fuckload of antisemitism as anyone who lived in the USSR could tell you. The USSR was just as racist as every other European nation.