If it was a bona fide investment and you are without notice of any wrongdoing - no, I’d say you’re not. Presumably your nefarious investor holds some kind of ownership interest that can be sold by their trustees/liquidators to raise funds. If you are able to do so, it seems like a nice thing to try to help source money to help the people caught out, including by assisting in realising any ownership stake, but that’s a choice, not an obligation.

Edit: to avoid ambiguity, this response is written re morality, not legality.