...last week he spent 36 hours in police custody, sleeping two nights in the headquarters of a special art-theft squad outside Paris, where he was formally charged with concealing art that had been reported missing or stolen.

The crime, known officially as a “breach of trust,” carries a maximum penalty of seven years in prison.

In the course of his questioning Mr. Wildenstein made a surprising claim: He told the police that the institute, which specializes in gathering detailed information about art for scholars, lacked any inventory for a roomy vault where dozens of valuable artworks that it does not own were discovered this year by the police.

“I didn’t inspect the vault,” Mr. Wildenstein said, according to internal court records of his questioning by an investigative judge while in custody. “We have never had an inventory of the vault.”