For the past couple of years, prosecutors in Germany have been investigating a massive trove of suspected looted art.

Back in 2012, police discovered some 1,400 paintings, drawings, and other artworks stashed in an apartment in Munich. The place belonged to a reclusive 81-year-old man named Cornelius Gurlitt, the son of one of Hitler's four major art dealers, Hildebrand Gurlitt. And his collection included paintings, drawings and sketches looted by the Nazis during World War II.

But Wednesday, the case took a surprising twist: Prosecutors announced they're giving most of the art back to Gurlitt. At the same time, they're giving anybody with a credible claim on a piece one year to prove it.

Wall Street Journal reporter Mary Lane, who has been covering the somewhat complicated story, says the senior Gurlitt was so successful that Hitler had planned for him to be the director of his Führermuseum

"[It] was going to have lots of looted art and be located in Linz, Austria, but of course he lost the war and that never happened," Lane said.

After the end of World War II, Lane says Hildebrand Gurlitt gave some of his artworks to the Monument Men to investigate, "but he hid a lot of it actually, he gave some to a friend in Switzerland, he hid some in a windmill, he didn't really disclose the whereabouts of all of the work, and his son inherited it when he passed away."

Cornelius Gurlitt stored much of the art in his Munich apartment. "He's never really had any friends, he's never been married or dated anyone by his own admission, so he's really lived under the radar in Germany till this collection was discovered by tax authorities," Lane said.

The collection includes works by high-profile artists including Chagall, Klee, Liebermann, Picasso and Toulouse-Lautrec. Perhaps the highest profile painting in the collection is a portrait of a woman with a fan by the French master Matisse. According to the Lost Art Internet database, it belongs to the family of Jewish art collector Paul Rosenberg. The family says the work was stolen from a bank vault in France during a 1941 raid carried out by the Nazis. It's estimated the painting might fetch as much as $20 million at auction.

It was surprising, then, when German officials this week announced they'd return the Matisse painting, along with much of the rest of the collection, to Gurlitt even though everyone knows it was stolen. Lane says there are a couple of explanations.

First, the work was confiscated two years ago by German authorities as part of a tax probe. But Lane says Gurlitt's attorney has pointed out to authorities that despite two years of investigation, they haven't come up with any evidence of violations. The attorney has challenged the authorities to either charge Gurlitt with something or give the art back.

Secondly, Germany has a statute of limitations for art stolen by individuals. "Whether it was art looted during World War II from Jews or homosexuals or political dissidents, it is the same as art that's stolen today," Lane says. "That’s 30 years, so the statute of limitations expired in the 1970s, which is not the case in a lot of European countries." Lane calls it's remarkable that Germany has a statute of limitations for art stolen by the Nazis. It's been hotly debated in Germany.

But the case of Cornelius Gurlitt is far from over. The fate of individual pieces in the collection will be determined over the coming year, as claims are assessed.

"Watch for what happens next between the Rosenberg family, who's claiming the Matisse, and Gurlitt's lawyers," Lane says. "The two sides were close to a deal last week, but at the last minute the German task force looking into the provenance of this art collection jumped into the picture and said there was a third-party claim."

It boils down to is this, Lane says. If there is no legal requirement for Gurlitt to return the Matisse, "will Gurlitt be true to earlier pledges made to give the art back to its rightful owners or will there be more wrangling and attempts at getting some kind of monetary compensation for it?"

Updated: A previous version of this post incorrectly cited Matisse as an Impressionist master. He's more closely associated with Fauvism. Thanks to listeners for pointing that out.