Is it obligatory to return money that was withdrawn from funds exceeding the principal from a person who was proven to be a swindler after dealing with him on the basis of trust, and what is the ruling on what was spent from those funds before knowing the truth about this person?

You must return any amount exceeding the principal, because it has become clear that the man unlawfully seized people's money, and what he gave you was not a true profit. Your ignorance removes the sin, but it does not remove the obligation of guarantee. You must pay what you can now, and the rest remains a debt upon you.