Just before the most prestigious U.S. art fair, Art Basel Miami Beach, opened in December, an energetic 70-year-old man named Asher Edelman marched through the local convention center to the booth of a Zurich gallery. He was accompanied by a dozen U.S. marshals. As onlookers whispered, the marshals seized four paintings by Yves Klein, Fernand Leger, Joan Miro and Edgar Degas worth around $15 million (10.75 million euros).

Mr. Edelman goes to great lengths to protect his art interests. He had gotten a U.S. federal court order to confiscate the Zurich gallery's inventory as potential compensation for a $750,000 Robert Ryman painting that the gallery, called Gmurzynska, had borrowed from him and, he says, accidentally damaged.