Leaving aside non-legal, but real practicalities and concerns, such as whether you want to use the real name of a secretive and rich person who comes from a nation with a weak concept of the rule of law and jucstice:1) If you say anything that could be taken as a factual assertion which damages his reputation, the oligarch could sue you for defamation. While the truth is a defense to a defamation claim--i.e. it's only defamation if its false; a true factual assertion might be unflattering or damaging, it is not defamation--it can often be difficult, especially with secretive people, to prove the truth of your assertions.2) Depending upon what information you do divulge and how it is obtained, it is possible that some of it may be give rise to an invasion of privacy claim.This is probably a dangerous thing to do on several levels.