So there's one more step to being a billionaire after getting the assets. You have to have not spent/lost them yet. That's the hard part that takes the self control, I think.
(And it's pointless self control because there's no reason to be a billionaire. So you could just give it all away.)
If they are billionaires and didn't commit crimes (that we know of) then they are just smart rich people.
If they committed crimes while becoming or being rich, then they were just silly criminals.