Bavarian tax authorities investigating Cornelius Gurlitt’s affairs one day in 2012 were startled by the contents of his Munich apartment, art piled floor to ceiling — 1,280 pieces, when they counted.

Eventually they understood they had blundered on a piece of history: Much of this was art stolen by Nazis, in most cases from Jews. Gurlitt was the son and heir of Hildebrand Gurlitt, a Hamburg art dealer who fenced stolen art. Hildebrand squirrelled away many pieces for himself, and left them to his son.

The grandeur of traditional German culture collapsed into barbarism under Nazi policies, famously in their treatment of art. The squalid cultural legacy of the Nazis is largely forgotten — few even remember that they commissioned anti-Jewish movies — but decades from now the world will still be talking about the way the Hitler government treated painting. The story keeps re-appearing, sometimes in major revelations like the Gurlitt affair.

On one level the Nazis appointed themselves censors who determined which art was suitable for viewing by the New Germans and which was so degraded that it could be used to fire up their nationalist racism in campaigns against “degenerate Jewish art.”

At the same time the Nazis turned themselves into thieves who stole every masterpiece that wasn’t nailed down, sometimes forcing desperate Jews to sell at bargain rates, sometimes just grabbing the stuff. Museums have since been discovering to their embarrassment that they hold art that belonged to people later killed at Auschwitz. Many illegally acquired paintings have never been recovered by rightful heirs. Many more can be expected to appear in future.

A fresh light fell on these crimes this year when Cornelius Gurlitt died, age 81, and left all his art to the Bern Kunstmuseum in Switzerland. More works were found in his home in Salzburg, including a Cezanne painting of Mont Ste.-Victoire, a Paris cityscape by Camille Pissarro, a Monet view of Waterloo Bridge and a highly desirable Gauguin. So the museum received about 1,500 paintings and drawings.

They are being studied and the museum has agreed to accept only art that’s unlikely to have been acquired illegally. For now the art is in the hands of a sub-speciality of art scholarship, “provenance research.” In this niche museum job, scholars typically combine a PhD in art history with the suspect-everything attitude of a good detective. They comb through 80-year-old auction catalogues and the records of dealers, taking special note of transactions between 1933 and 1945.

The Centre for Provenance Research in Berlin is helping develop this scholarship in 90 locations in art museums and universities. The German government maintains The Lost Art Database (www.lostart.de) in Magdeburg to document cultural objects that were seized from private owners as a result of persecution under the Nazis. It has a list of 29,000 suspected works in public collections with dubious provenance and a separate list of art objects that potential heirs hope to recover.

Hildebrand Gurlitt prospered during the Hitler era and stayed in business many years after the war ended. So did several other dealers. Bruno Lohse, a captain in the SS as well as an art historian, served in German-occupied Paris for several years. He helped the head of the German air force, Hermann Göring, to amass his large personal collection, he selected Old Masters for the museum Hitler planned to build at Linz after the war, and he added to his own holdings. In May, 2007, when Lohse died, his private vault in a Zurich bank contained many pictures, including a major Camille Pissarro painting the Gestapo had stolen from a Jewish publisher in Vienna in 1938. Jonathan Petropoulos, an American author who wrote Art As Politics in the Third Reich, concluded that Lohse continued to sell plundered art in the last years of his life. In the 1980s and later, at least 14 paintings left Lohse’s stash, including work by Corot and Dürer.

Since 1998 the German federal government has committed itself to returning stolen art to the original owners or their heirs. But in recent years, without much publicity outside Germany, new villains have been revealed. A recent article from Deutsche Welle says that East Germany acquired Western currency it needed by having its Stasi secret police systematically seize art from individuals. Real owners of the art, armed with evidence, are starting to turn up in the courts, demanding restitution. Provenance research, having experienced a boom in the shadow of the Nazis, may turn out to be a permanent scholarly enterprise.