BERN - A Swiss museum director preparing for a Naziera art collection's long-awaited public unveiling later this year said Friday that her goal remains finding heirs to any works that may have been looted from Jewish owners.

Bern Museum of Fine Arts head Nina Zimmer, who took ownership of 150 drawings, lithographs and paintings this week ahead of an exhibition slated to begin in November, said research shows none of these were stolen by National Socialists.

But questions linger over the provenance of some of the collection's pieces still in Germany, where a 2012 raid by authorities on a Munich apartment produced a sensation: 1,500 long-lost works by modern masters, including Pablo Picasso, Otto Dix and Henri Matisse.