because he wants to keep his money together and dont want to lose money. But thats only a guess of course.
I don't get why keeping hostage users' assets is related to "his" money. Supposing that he's going to ask for a ransom?
Because when he now releases all the remaining usermoney he has access to and the asset info he has no pressure object anymore to get the double payment back. Because it was his error he would have to pay form his money. But he dont want this. So he stops everything to take hostage what he has to get this money back so that he dont have to pay it from his own money later.
Of course thats somewhat dangerous because he holds things that arent his. He should realize that the bigger threat to him isnt losing money but the government involved. On the other hand... the person that involves government will make it more difficult for all parties.