BERLIN — An investigation into suspected tax fraud has uncovered a vast trove of artwork seized by the Nazis before World War II and kept behind pallets of canned goods in the Munich apartment of a 79-year-old man whose father was once a dealer in pirated art.

The collection is believed to include works by Pablo Picasso, Henri Matisse, Pierre-Auguste Renoir and Marc Chagall, among many others. Estimates of its value top $1.3 billion.

Officials kept the collection’s discovery quiet for two years, uncertain who were the rightful owners of the works and whether a crime had been committed. It finally became public over the weekend, when the German news magazine Focus broke the story.

Prosecutors and the art historian who has been cataloging the collection refused to discuss details of the case Monday, but said more details would be forthcoming at a news conference scheduled today.

The man who had been in possession of the collection had been supporting himself for decades by occasionally selling a piece.

In all, the collection contains about 1,500 art works. How such a vast collection could remain secret for so long puzzled many in the art world.

“I can only think that we in the art world are too naive to look for criminality in those dealing in such works of beauty,” said Austrian art expert Gert Kerschbaumer. “There is no other way to explain why this collection, sold a piece here and there, went unnoticed for so long. Unless it was corruption from both art dealers and those in seats of power.”

Determining who has a valid ownership claim to the art is likely to be a complicated affair.

Some pieces are thought to have followed the tragic path of Nazi art plunder: seized by the Nazis from the private collections of Jewish families and collectors or forced to be sold at bargain prices. The heirs of those former owners would have a claim to the art, if they can be located.