Can I go over to Martha’s and steal all her stuff while she’s in jail? 
I got dibs on the festive holiday centerpieces!
Matha’s stuff still belongs to Martha. I assume she’ll have a caretaker, and probably a few rotweillers roaming the estate.
IIRC some of what happens to it depends on the crime of which they’re convicted. There are laws which require the disgorgement of any profits illegally obtained in some crimes, and others which allow for forfeiture of property used in the act of commiting the crime (i.e. seizing a car used in a drug buy or to pick up a prostitute), even if the property in question doesn’t belong to the person who commited the crime. If there are fines involved I think that assets can be seized and liquidated to cover the fines but I’m not 100% on that. Certainly the IRS can go into bank accounts and garnish wages to satisfy tax delinquncies and presumably can do the same in cases of tax fraud.
With all due respect to Otto’s fine and factual answer, I’ve so rarely seen a rich person go to jail that I wasn’t sure there would be a factual answer.
Don’t mind me, I’m feeling very cynical today.