Lawyers who broker the return of artworks for "finder fees" have also ended up facing charges themselves.
Mr. Hirschfeld had also sought the return of artworks consigned to the Margo Feiden Galleries, said to number 1,000 to 1,200.
Yves Rouart, nephew and heir of the art collector Anne-Marie Rouart, has been battling the Wildensteins in the French courts for years for the return of artworks from Mrs. Rouart's collection after her death in 1993.
While there was a federal compensation law prescribing the return of artworks looted or sold under pressure in the immediate aftermath of the second world war, no such law is still legally binding today.
The other was a little-noticed decision by a federal court in California in a case brought by an American citizen against Austria for the return of artworks lost by her family during the Holocaust.
Although Marinello said the Rosenberg family were grateful to the German authorities, the Bern museum and the Gurlitt heirs for their help in returning the work, he said the returning of artworks to descendants could be handled better.
They promote the return of such artwork and artifacts.
One trustee demanded the return of donated artwork, intending to find it a more deserving home.
Suing for fraud and breach of contract, Ovitz is seeking the return of the artwork, along with unspecified compensatory and punitive damages.
Mr. Wildenstein said, "The heirs had not asked for return of the artworks, otherwise I would have returned them".
