It is an open secret in the art world but now the Helly Nahmad gambling case seems to have tipped off the New York Times:

Most of these industries have checks. Real estate titles and deeds at least require a name. Mortgage brokers, stockbrokers, casinos, banks and Western Union must report suspicious financial activity to the federal Financial Crimes Enforcement Network. Banks must report all transactions of $10,000 or more. Altogether, the network logs more than 15 million currency transactions each year that can be used to track dirty money, said Steve Hudak, a spokesman for the agency. The art market lacks these safeguards. Roll up a canvas and it is easy to stash or move between countries; prices can be raised or lowered by millions of dollars in a heartbeat; and the names of buyers and sellers tend to be guarded zealously, leaving law enforcement to guess who was involved, where the money came from and whether the price was suspicious.

Valuable as Art but Priceless as a Tool to Launder Money (New York Times)