A Ponzi scammer gives his early investors a great rate of return. It's all investor money anyway. If you have celebrity investors, you make sure you give them a good return to get the word of mouth going for you.
At some point, of course, because there are no real investments being made with all the investor money coming in, you couldn't straighten up and fly right if you wanted to. All these people out there think they own something now and they don't. So you disappear.
Slatkin forgot to do the last step. (It's probably getting harder to do a good disappearing act these days.)
Anyway, it's very, very unlikely Greta knew anything.