Masurovsky often turns to Spiegler to discuss thorny legal and ethical questions. And there are plenty of those, often raised by an artwork's inadequate "provenance," or proof-of-origins. In the art world, that's the paper trail that proves a painting or sculpture is not forged or stolen. Masurovsky says Spiegler's work has created a new sense of moral and legal responsibility in the art-collecting community .

This month, Spiegler and his art law colleagues at Herrick, Feinstein in New York settled one of art law's most vexing, prolonged cases for the heirs of a Jewish Austrian art dealer.

In 1938, the year Austria was annexed into Hitler's Third Reich, a Nazi party member stole the Vienna dealer's property, the painting "Portrait of Wally."

The work ended up in a Vienna museum, but was seized by the U.S. government while it was on loan to the Museum of Modern Art in New York. Spiegler's firm won a $19 million settlement for the heirs.

The Vienna museum will retain the painting, but the display will now include signage indicating its Nazi-looted past.

Spiegler's firm successfully represented the heirs of Russian artist Kazimir Malevich in their litigation against the City of Amsterdam. Five Malevich paintings were returned to the artist's heirs.

Stolen treasure

In 1993, Spiegler earned the gratitude of the Republic of Turkey for recovering 6th century gold and silver treasures which had been stolen by tomb raiders and eventually sold to New York's Metropolitan Museum of Art.