And here's another maybe. Navalny, in his YouTube doc series, Putin's Palace, makes the claim that Vlad's the richest person on earth, worth (before the Ukrainian fiasco) roughly $1T.
And Browder makes the case in his various books that with a yearly salary equal to $300K, Putin needs to stash his money somewhere in order to not seem like the biggest thief on the planet, which he clearly is (putting aside the Windsors, ahem).
For example, there's a run of the mill violinist in the Moscow Symphony, a close childhood friend of Putin's from middle class origins, who claims a net worth of $200M. He's clearly sitting on one pile for his old pal.
With the Magnitsky Act making it hard for Vlad to get at a lot of his money, it seems possible that Bout is also holding a pile for him that couldn't be accessed while Bout was in prison.
Sorry, gotta run, no time for posting links, but none of this is hard to come by or are figments of my overactive imagination.