Quote Originally Posted by Marcus View Post
Is it really proved that he was in a Soviet jail and was killed there?
not with 100% certainty, but at least some of his personal belongings were uncovered in Russia and given the fact that nobody knew anything about him until they were uncovered is a good indication he wasn't a free man in Russia
but whether he was murdered or died of natural causes isn't decided upon, autopsy wasn't conducted and probably for a good reason

you can read some on WIKI