(NYTIMES) - The federal agents who raided a drug dealer's house in a suburb of Philadelphia found marijuana and, to their surprise, US$2.5 million (S$3.4 million) in cash stashed in a secret compartment beneath a fish tank.
But they were even more surprised to discover so much art - 14 paintings on the walls and another 33 stacked in a storage unit a few kilometres away from the home of the dealer, Ronald Belciano. The artists included Renoir, Picasso and Salvador Dali.
"That jumped out at us," said Mr Brian Michael, special agent in charge at Homeland Security Investigations Philadelphia. "That amount of artwork was not something you come across in every investigation."
It turned out that Belciano used the art to launder some of his drug cash, purchasing the works from an established gallery near Philadelphia's Museum Row.
In 2015, he was sentenced to more than five years in prison for dealing drugs and for laundering the illicit proceeds by taking advantage of one of the art market's signature features - its opacity.
Art worth billions of dollars changes hands every year with little or no public scrutiny. Buyers typically have no idea where the work they are purchasing is coming from. Sellers are similarly in the dark about where a work is going.
And none of the purchasing requires the filing of paperwork that would allow regulators to easily track art sales or profits, a distinct difference from the way the government can review the transfer of other substantial assets, like stocks or real estate.
But now the authorities who fear that the Belciano case is no longer an oddity, but a parable of how useful art has become as a tool for money launderers, are considering boosting oversight of the market and making it more transparent.
In January, the US Congress extended federal anti-money-laundering regulations, designed to govern the banking industry, to antiquities dealers. The legislation required the Department of the Treasury to join up with other agencies to study whether the stricter regulations should be imposed on the wider art market as well.
The US effort follows laws recently adopted in Europe, where dealers and auction houses must now determine the identity of their clients and check the source of their wealth.
To art world veterans, who associate anonymity with discretion, tradition and class, not duplicity, this siege on secrecy is an overreaction that will damage the market. They worry about alienating customers with probing questions when there is scant evidence of abuse.
While there is no evidence of widespread cheating involving art, experts say it is clear the secrecy of the market creates vulnerabilities for an enforcement system that rarely conducts audits and relies heavily on the willingness of collectors to make plain their profits.
"The only ones who know," said Professor Khrista McCarden of Tulane Law School, who specialises in the tax code, "are you, the art gallery and God."
The secrets of the art world sometimes tumble out at places like the Eden Rock hotel on St Barts, where at a lunch in 2014 overlooking the turquoise waters of St Jean Bay, Russian billionaire Dmitry Rybolovlev, a collector, was introduced to New York art adviser Sandy Heller.
Mr Rybolovlev had paid $118 million for a Modigliani nude from an unknown seller. Mr Heller confirmed that the seller had been his client, the hedge fund manager Steven Cohen. But something was off. Mr Cohen had charged only $93.5 million, Mr Heller said.
Mr Rybolovlev has alleged in multiple court cases that he was defrauded when he used a man he said he believed he had hired as an art adviser, Yves Bouvier, to make that and many other purchases, totaling nearly $2 billion. According to the suits, Mr Bouvier was buying the works at one price and flipping them at huge markups to Mr Rybolovlev.
Mr Bouvier, who has prevailed in several of the lawsuits, has said it was always clear he was operating, not as an adviser, but as an independent seller who could buy the art and resell on his own terms. But in the legal battle that has ensued, Mr Rybolovlev has castigated not only Mr Bouvier, but the art world itself.
“If the market were more transparent, these things wouldn’t happen,” he said.
Auction houses, for example, today publish estimates of prices they expect artworks to achieve. Auction catalogues say works are from "a private collection", often nothing more.
Paintings are at times brought to market by representatives of owners whose identities are unknown, even to the galleries arranging the sale, experts and officials say. Purchasers use surrogates, too.
When Mr Rybolovlev sold Leonardo da Vinci's Salvator Mundi to Saudi Crown Prince Mohammed Salman, for example, it was bought by a friend of the prince, which obscured who was shopping.
In these circumstances, the galleries rely on the integrity of the agents, with whom they have long done business. Sometimes the buyers and sellers are not individuals at all, but shell companies, opaque investment structures often designed to conceal identity.
"The variety of frauds in the art world is almost infinite and that is facilitated by the fact that the art world operates with a secrecy that no other investor would dream of operating in," said Professor Herbert Lazerow of the University of San Diego School of Law.
Antiquities dealers are concerned about the cost of complying with anti-money-laundering regulations. They say they know their customers well enough to know they are not engaged in illicit activities.
Auction houses have responded to the changes in Europe with more thorough vetting of their customers in the United States, too. Christie's says sellers at its New York auctions must fully disclose their identity. For buyers, it says it verifies the identity of any agent and works to identify the sources of funds when there is any suggestion of risk.
How much money laundering involves art? No one seems to have quantified it, though many experts agree the art market is a natural place for it to flourish.
"Pieces are portable, there is a high level of secrecy around who owns what and the value they're paying, and it's debatable in some ways," said Ms Nienke Palstra, a researcher at non-governmental organisation Global Witness.
Still, the number of prosecutions that have been made would not, by itself, suggest the problem is ubiquitous. Some experts say enforcement efforts have simply been too anaemic to detect laundering, and that the size of the problem will become apparent if dealers and auction houses are required to report suspicious activities.
"You don't know what you don't know," said Mr Peter Hardy, a former US prosecutor.