“We have not been contacted by the U.S. authorities and are unaware whether -- or how -- any such inquiry has been initiated,” said Daniel Levy, an attorney for Bouvier at McKool Smith in New York. “During the course of this commercial dispute over paintings, the other party has repeatedly attempted to use law enforcement to further his own private objectives.”

A spokesman for Rybolovlev didn’t immediately comment. A Justice Department spokesman declined to comment.

Monaco Penthouse

Until now, this drama has unfolded mostly in Monaco, where Rybolovlev, 49, lives in one of the world’s most expensive neighborhoods, in a penthouse that overlooks Monte Carlo’s yacht-filled marina.

It was in Monaco last February that police arrested Bouvier as he entered the lobby of Rybolovlev’s Belle Epoque residence. Bouvier denied the allegations in the Russian billionaire’s complaint that Bouvier misled Rybolovlev about the prices of works he was buying. In November, an appeals court rejected Bouvier’s request to have the criminal charges of fraud and complicity in money laundering against him dropped, and Rybolovlev said in a statement that he was “pleased” that the case was going forward.

One of the masterpieces Bouvier procured for Rybolovlev was none other than “Salvator Mundi,” a 16th-century painting of Christ. With its authorship unclear, the painting was acquired by a consortium of art dealers that included Robert Simon, a specialist in Old Masters. Simon then brought the painting in 2005 to Dianne Modestini, a renowned restorer and research professor at New York University in Manhattan.

Yellowing Varnish

Modestini recalls placing the oil painting on an easel in her Upper East Side studio. It was covered with yellowing varnish and overpainted from previous restoration attempts. Modestini began painstakingly restoring the piece. It wasn’t until years later that she knew for sure that she had restored one of the rarest pieces of art in the world.

Experts now agree Leonardo painted the piece for Louis XII of France, probably around the year 1500. Following the discovery, the painting was exhibited in London’s National Gallery.

Then, in 2013, a mystery buyer acquired “Salvator Mundi.” It was Rybolovlev, according to later news reports. He purchased the painting, via Bouvier, though a trust. According to the Monaco complaint, the billionaire paid $127.5 million for the work, which was roughly $50 million more that he later said the seller had received, alleging Bouvier pocketed the difference.