@gemlog Political assassinations are a plausible theory. They have never been viewed as something unthinkable in Russia, after all we've had a few good examples, like Litvinenko, Politkovskaya and the more recent ones: Nemtsov, The Skripals, Navalny's assassination attempt. Some happened domestically so were never properly investigated, but no one believes official version of course. Berezovsky's "suicide" was underinvestigated, but the consensus is that it's also one of such cases.
@gemlog As stated in the article, there are a lot of "mysterious" suicide cases among businessmen and they are happening more and more often, I can't pick any from top off my head, but it happens to high-ranking "siloviki" too, even if some of these suicides and accidents weren't staged, no one's against treating them as assassinations. It's evident that Putin got EXTREMELY paranoid as of recent, him using this as a tool to keep his inner circle in check isn't hard to believe.
@gemlog There were a few phone conversations leaked recently hinting that he's getting unpopular even among business elites — no wonder, when their own wealth is in danger due to sanctions. Yet, we aren't seeing any defections, looks like scaring them to "hold the line" works quite well.