From left, a Etruscan sarcophagus that was locked in a free port for decades under a shell company’s name and returned to Italy earlier this year along with other antiquities stolen from burial sites; Picasso’s “Petit Pierrot aux Fleurs,” a portrait of his son Paolo in a harlequin costume, one of about 4,500 works the Nahmad family of London art dealers is said to have tucked away in the Geneva Fr