He filed the lawsuit in 2005 after learning the painting was on display at the Thyssen-Bornemisza Museum after the foundation rebuffed his other efforts to have the painting returned.
The dispute before the Supreme Court turns on how federal courts should decide -- under the Foreign Sovereign Immunities Act, which sets limits on when a foreign entity is immune to litigation -- whether to apply a state law or the law of the foreign country.The Cassirer family -- now being led in the litigation by Claude's children after Claude died in 2010 -- are making claims under a California law that they say makes them the rightful owners of the painting, because of how the artwork was obtained.