BERLIN -- A Swiss museum accepted a massive, priceless trove of long-hidden art from the late German collector Cornelius Gurlitt on Monday, promising to work with Germany to make sure that any Nazi-looted pieces in it are returned to Jewish heirs.

Three works in the collection donated to Switzerland's Kunstmuseum Bern will be returned immediately because they have already been identified as looted art, German Culture Minister Monika Gruetters said at a joint news conference with the museum. The pieces are by Henri Matisse, Max Liebermann and Carl Spitzweg.

Germany, meanwhile, published online the business ledgers of Gurlitt's father Hildebrand, an art dealer who had worked closely with the Nazi regime. Many potential heirs and art experts had demanded the move to help their searches for possible looted art. The ledgers covered the years from 1937-45, detailing in neat fountain pen the purchases and sales of various paintings.

Monday's press conference was the latest twist in a saga that has captivated the art world.

In 2012, German authorities seized 1,280 pieces of art from Cornelius Gurlitt's Munich apartment while investigating a tax case, including works by Pablo Picasso and Marc Chagall. The development shocked the art world, since many of the works had not been seen for decades and experts feared they had been lost or destroyed.

Gurlitt said he had inherited much of the art from his father, who in the 1930s helped the Nazis sell art they considered "degenerate" to buyers outside of Germany for cash. Some of the works -- including Impressionist and modern masterpieces -- had been seized by the Nazis from museums, while others were stolen or bought for a pittance from Jewish collectors who were forced to sell.

Gurlitt died in May at age 81, designating Switzerland's Kunstmuseum Bern as his sole heir.

A special German government task force that was already looking into the provenance of the Gurlitt art will now work closely with the Kunstmuseum Bern to return any looted art as quickly as possible, Gruetters said. The agency is checking about 240 art works in the Munich trove that may have been looted by the Nazis.

"As part of our special German responsibility toward the victims of the Nazi dictatorship, we want to ensure justice is done not only in the legal framing of the agreement, but also morally," Gruetters said.

In addition to art in Munich, more than 200 artworks were found at Gurlitt's house in Salzburg, Austria. Details on the Salzburg art have been scarce -- it's not even clear where the art is now stored. Gruetters said it will be checked to see if it, too, contains Nazi-looted art.

One of Gurlitt's cousins has filed a claim on the collection, which a Munich court said would have to be sorted out before the art goes anywhere. The court has given no indication of how long that could take.

Kunstmuseum Bern's board president, Christoph Schaeublin, told reporters the decision to accept the collection came only after long, difficult deliberations to figure out how the museum could carry out the responsibilities that came with the bequest.

Julius Schoeps, a prominent German-Jewish scholar who believes art stolen from his family may be among the Gurlitt collection, told The Associated Press he welcomed Germany's move to put Hildebrand Gurlitt's account books online. But Schoeps said the new agreement seems to make it even more complicated for possible heirs to retrieve their property.

"They didn't say a word about who we can turn to for help," said Schoeps. "More and more institutions are getting involved in this -- the German government task force, the Bern museum, the Lost Art Database in Magdeburg -- I find this very irritating."

Greg Schneider, executive vice-president of the Conference on Jewish Material Claims Against Germany, said so far the work of the German task force on looted art has been too opaque. He urged that the agency make both its deliberations and its findings public.

"The major aspects of the agreement are quite positive, the key will be the implementation," Schneider said in a telephone interview from New York. "This promises lifting the veil of secrecy, so we'll have to see."