Authorities seeking illegally acquired antique artworks have searched the apartment and office of prominent New York billionaire and philanthropist Michael Steinhardt, prosecutors said.

As many as nine pieces were reportedly seized. Steinhardt, 77, made his fortune as a hedge-fund manager and is known as a major philanthropist to Jewish and Israeli causes, including as a co-founder of Taglit-Birthright.

A spokesman for Manhattan district attorney Cyrus Vance Jr. would neither confirm nor deny the seizures Friday but did confirm the searches. Vance has been active for years in trying to repatriate stolen artworks.

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Steinhardt is a well-known collector of Greek antiquities and even has a gallery named after him and wife Judy in the Metropolitan Museum, not far from their Fifth Avenue apartment. Steinhardt told The New York Times he had no comment on the matter “for now.”

Copies of search warrants provided to AFP, and signed by a New York judge on January 3, indicated that investigators were seeking about a dozen antiques from Greece and Italy, acquired between 1996 and 2011 for sums ranging from $25,000 to $380,000.

The latter sum was spent in 2006 to acquire an 18-inch (45-centimeter)-tall white oil vessel that depicts the figures of a woman and a young boy in a funerary scene dating from around 420 BCE.

A spokesman for the prosecutor’s office would not say whether Steinhardt might face any charges, but the search warrants list criminal possession of stolen property as a potential violation.

Steinhardt — a prominent philanthropist and co-founder of the Birthright program, which has funded fully subsidized 10-day trips to Israel for more than 500,000 young Diaspora Jews — was one of the two first non-Israeli citizens to light a torch at Israel’s official Independence Day celebrations on Mount Herzl earlier this year.

He has donated tens of millions of dollars to Jewish causes, including through the Steinhardt Foundation for Jewish Life and a number of educational institutions.

His most recent major gift to Israel was the 8,000-square-meter (26,250-square-foot) Steinhardt Museum of Natural History, Israel National Center for Biodiversity Studies, at Tel Aviv University.

He is thought to be one of a several shareholders in an anonymous company that last year purchased several acres of former Greek Patriarchate land in the Jerusalem neighborhoods of Givat Oranim and Old Katamon.

In 2013, his 500 piece Judaica collection was auctioned off for $8.5 million, the “most valuable auction of Judaica ever held,” Sotheby’s said at the time.

In recent years, Vance’s office has made it a priority to track stolen works — seizing some from museums, private collections or auction houses — and return them to their rightful owners, including in Lebanon, Pakistan and Italy.

So far, no charges have been brought against anyone for possessing the disputed works — which sometimes pass through several hands before reaching owners in New York, the Times said.

Thus, on December 15 three antiques were returned to Lebanon. They included a Greek bull’s head statue that had been exhibited at the Metropolitan Museum of Art. Its estimated value: $1.2 million. Vance’s office said it had been stolen during Lebanon’s civil war.

Vance said at the time that his office had, since 2012, tracked down several thousand antique pieces with a total value of more than $150 million.