It started with a routine check by German tax inspectors - and resulted in the discovery of an art hoard so vast and spectacular that no one yet knows how the story truly ends.
On a high-speed train from Zurich to Munich on September 22, 2010, Germany's briskly polite officialdom was on the lookout for customs and tax cheats. Thousands of German citizens had bank accounts in Switzerland, many of them undeclared, and the route from Zurich was a prime target for those carrying substantial sums of cash.
One elderly man on the train raised their suspicions and prosecutors launched a preliminary tax probe against him.
Two years later, in February 2012, the trail led to the man's apartment in a wealthy district of Munich. Once inside, inspectors found a far more glittering prize than smuggled cash or evaded taxes: a huge collection of hidden artwork that sheds new light on some of the 20th-century's master painters and reawakens painful memories of Germany's Nazi past.
The paintings, drawings, engravings, woodcuts and prints numbered more than 1,400 in all and were created by an all-star roster of modern art: Marc Chagall, Henri Matisse, Pablo Picasso, Pierre-Auguste Renoir, Oskar Kokoschka, and leading German artists Otto Dix, Max Liebermann, Ernst Ludwig Kirchner. At least one older work was in the trove: a 16th-century engraving of the Crucifixion by Albrecht Duerer.
Some pieces - ones by Matisse, Chagall, Dix - were previously unknown, not listed in the detailed inventories compiled by art scholars.
Investigators' excitement at the find was tempered by a disturbing question. At least some of the works had apparently been seized by the Nazis - so who were they taken from and who now are their rightful owners?
At a news conference in Augsburg, Germany, prosecutors wouldn't identify the elderly suspect, citing tax secrecy laws and the ongoing investigation. They did say he hasn't asked for the artwork back and that they were not currently in contact with him.
Prosecutors are probing whether he improperly acquired the works, but no charges have been filed and prosecutors say there may not be any.
Although prosecutors didn't name the suspect, heirs of the late Jewish collector Alfred Flechtheim issued a statement saying the case raised "justifiable suspicions" that some works the Nazis had taken from him might have been bought by Hildebrand Gurlitt, an art dealer who acted for the Nazis.
A Max Beckmann painting that once belonged to Flechtheim was sold two years ago through the Lempertz auction house in Cologne. A legal adviser for Lempertz, Karl-Sax Feddersen, told The Associated Press that the seller was Gurlitt's son Cornelius.
The German magazine Focus also reported that Cornelius Gurlitt was the man under investigation.
Neither Cornelius Gurlitt nor his lawyer could immediately be reached for comment.
The mystery now turns to the art.
The 121 framed and 1,285 unframed works found in one room at the apartment were "professionally stored and in a very good condition," said Siegfried Kloeble, head of the customs investigations office in Munich. He said it took a specialist company three days to remove the paintings; officials refused to say where they are being kept now.
Investigators, aided by a leading art historian, are trying to establish the artworks' legal status and history. So far, officials said they have done at least preliminary research on only about 500 of the pieces.
It's unclear how many of the works might be subject to return to pre-World War II owners.
Speaking at the news conference, prosecutor Reinhard Nemetz said investigators have turned up "concrete evidence" that the find includes both works that the Nazis classed as "degenerate art" and seized from German museums in 1937 or shortly after, and other works that may have been taken from individuals. The Nazis often forced Jewish collectors to sell their art at pitifully low prices to German dealers or simply took them.
"Degenerate art" was largely modern or abstract works that Adolf Hitler's regime believed to be a corrupt influence on the German people. Many such works were later sold to enrich the Nazis. An art expert working with prosecutors said those sales are legally valid, even if other works in the collection may eventually be found to belong to survivors of Nazi persecution or their heirs.
The Conference on Jewish Material Claims Against Germany called for the works to be made public immediately so families of Holocaust victims could locate and recover art that had been taken from them. The conference also said that art for which heirs could not be found "must not remain with Cornelius Gurlitt, the son of a Nazi-affiliated art dealer who profited from art confiscated from Holocaust victims or sold under duress".
It said any unclaimed art should be auctioned and the money used for assistance to Holocaust survivors or Holocaust education.
Nemetz defended the delay in making the find public and rejected calls to make images immediately available on the internet to help potential owners, citing copyright and security concerns.
Art historian Meike Hoffmann, an expert on "degenerate art" at the Free University of Berlin, offered a glimpse of some of the works during a slide show at the same news conference.
She showed works she said had not been known to scholars, or known only from documents without any photos to give an idea what the works looked like.
"Such cases are of high importance to art historians," she explained.
One Matisse painting of a woman, seized by the Nazis in France during World War II, is not in the established catalogue of his works, she noted. A Chagall gouache of an allegorical scene also isn't among the artist's listed works. Experts haven't yet been able to determine where the Chagall came from, she said.
Other works, such as an unknown self-portrait by 20th-century German artist Otto Dix or a woodcut by Ernst Ludwig Kirchner, added new breadth to what's known about the artists, Hoffmann added.
Some were known works that appeared to have been legally sold, although their recent whereabouts may have been unknown. For instance, a previously listed work by Courbet of a girl with a goat made its way into the collection through an auction in 1949 - years after the end of World War II. A Franz Marc work, "Landscape with Horses," was identified as coming from an art museum in Moritzburg, Germany.
Overall, Hoffmann was elated with the quality and the depth of the find.
"When you stand in front of the works, see the ones that were long thought to have been lost or destroyed and in a relatively good state - some of them dirty but not damaged - you have an incredible feeling of happiness," she told reporters.
Five works from the art hoard:
German investigators showed images of some of the hoard of more than 1,400 art works they found at a Munich apartment. Here is a glance at some of the highlights.
"Two riders on the beach," a favourite subject of the German painter that recurs repeatedly in his work. Investigators didn't give details of the work's history. Liebermann, who was Jewish, quit Germany's Academy of Arts in 1933 after it decided no longer to exhibit works by Jewish artists. He died in 1935.
"Village girl with goat," one of two known paintings of the same subject by the 19th-century French realist. Art historian Meike Hoffmann, who is helping the investigation, said it was long considered to be lost. Documents show that it was sold at an auction in 1949, so it only found its way into the collection after World War II.
A self-portrait of the German expressionist and realist artist smoking. Hoffmann said she believes it was painted around 1919. She said the work was "completely unknown" to date.
A depiction of an allegorical scene that isn't contained in existing lists of work by the Jewish artist, who left France after the Nazi invasion, returned in 1948 and lived there until his death in 1985. Investigators haven't yet cleared up where the piece came from.
An untitled painting of a sitting woman that isn't included in existing indexes of Matisse's work. Experts date it to the mid-1920s, because the female figure and the room in which she sits are depicted in other Matisse pieces. It was seized by the Nazis from a bank in France in 1942.