After 36 hours in police custody and under questioning, billionaire art dealer Guy Wildenstein is sticking by his claim that he knew nothing about 30 missing paintings held in his family institute's vault in Paris. He was formally charged with concealing art that had been reported missing or stolen, which has a maximum penalty of seven years in prison.

A police raid uncovered the artworks---including a $1.1 million Berthe Morisot painting, Degas drawings and more---which heirs from various estates have been missing for decades.

Twenty of the recovered artworks belong to Suzanne Reinach, 98, who participated in the French Resistance and inherited the art from her aunt. She says she never received an estate inventory from Daniel Wildenstein, the father of Guy.

The accused art dealer, who is based in Paris and New York, maintains that there was no inventory for that vault room, which he blames on his late father as well as staffing reductions at the institute since 2001. Guy Wildenstein took charge of the institute in 2008 after his brother, Alec, passed away.

The Wildenstein Institute is an art reasearch center which publishes catalogues raisonnés for Monet, Manet and Gauguin.