NUREMBERG, Germany — After the last of the regular artworks, furniture and stamps were sold on a recent Saturday, Kathrin Weidler read a short statement absolving Weidler’s auction house of any moral responsibility for what came next.

Weidler, who is a director of the family-run business, then began the bidding for “Village on a Mountain Lake,” a run-of-the-mill watercolor, at 45,000 euros ($51,000). The picture seemed indistinguishable from thousands of watercolors sold at flea markets across Europe every week, except for the signature in the bottom right corner: “A. Hitler.”

In the last 10 years, the niche market for art by Hitler has grown, experts say, and this has led to an increase in the value of the paintings, drawings and watercolors supposedly created by the future dictator over a century ago. But many, if not most, of these works are likely not by Hitler. After years of letting such public auctions go unchecked, German prosecutors are starting to take notice.

Days before the auction in February, the district attorney’s office searched Weidler’s and confiscated 63 paintings: 26 scheduled for the sale, and another 37 apparently destined for future auctions. Antje Gabriels-Gorsolke, one of the prosecutors, said the art works were seized as part of an investigation into forgery and fraud.

And weeks before that, police interrupted a sale at the Kloss auction house in Berlin, where three paintings, also supposedly by Hitler, were on the block.

At Weidler’s in February, no one raised a paddle. Perhaps it was it was the presence of reporters in the room, the painting’s steep valuation, or the questions about authenticity that the raids had brought to the fore. The auctioneer demurely moved on to the next painting: “Mountain Landscape With Mountain Church and Haystacks,” also signed “A. Hitler.”

Hitler did most of his painting before World War I, after he was rejected from art school and before he volunteered for the German army. Once in power, he ordered the works to be collected, and he may have destroyed some of the more embarrassingly bad ones.

Beyond the moral question of buying poor art just because it was painted by a genocidal dictator, there is the problem of verifying whether Hitler actually made the works. So many fakes have been created and certified as real that no knows what the real Hitler paintings look like. And since they have no artistic value to speak of, there are few professional examiners willing to study them.

“It’s all part of a grubby gray-zone,” said Christian Fuhrmeister, an art historian at the Central Insitute for Art History, a state-funded research body.

“But I will say we get asked about it more frequently than in the past,” he said in an interview. Fuhrmeister said that all he and his colleagues can do is compare works with the few known Hitler paintings in the state archive of Bavaria to rule out the obvious forgeries.

The business of faking Hitler’s paintings dates back nearly to the first time he picked up a brush, said Bart Droog, a Dutch journalist who specializes in Hitler forgeries. By the time Hitler came into power in 1933, many fakes existed already, and both demand and supply grew over the years until, in 2014, a view of city hall in Munich, said to be painted by the dictator, was sold for $161,000, at Weidler’s auction house.

Gabriels-Gorsolke from the district attorney’s office said that prosecutors would investigate previous owners and sellers to see if fraud was committed. If fake, the pieces would then be permanently confiscated, but for now they sit in the police evidence locker.

With 63 works impounded and an estimated 100 already sold, Weidler’s has handled an eyebrow-raising number of them, especially given how few are likely to exist, said Sven Felix Kellerhoff, a historian and journalist for the newspaper Die Welt.

One of the confiscated works is a nude watercolor of Hitler’s niece, Geli Raubal, dated 1929, one of two versions of the same painting supposedly by Hitler. But both versions are almost certainly phonies.

And the other version illustrates how decades of imprecision and swindling have made it very difficult to sort out real Hitler paintings from knockoffs.

Marc-Oliver Boger, an expert in art forgery and collector of known fakes, said that version was made by Konrad Kujau, a convicted German forger who became famous in the 1980s after he admitted to falsifying diaries by Hitler that were published in the magazine Stern.

But the Kujau watercolor fooled people long enough that it made it into a 1983 catalog of Hitler’s works created by the American Billy F. Price. As well as faking the diaries, Kujau, who died in 2000, also faked art works in Hitler’s name, many of which made their way into the Price catalog, according to Boger.

To authenticate works in his catalog, Price had relied on the judgment of August Priesack, an art expert who was later discredited. Priesack had also authenticated the diaries (and “Village on a Mountain Lake,” the painting that went unsold at the Weidler’s auction, though that painting had not been confiscated by the authorities).

Unreliable as it is, the Price book is still used by many as the definitive catalog of Hitler’s art.

Weidler’s auction house did not respond to requests to comment for this article. But in 2016, Weidler, told a German radio station that the buyers of the works are not necessarily sympathetic to the Nazis. “There are many people who want to make an investment, and just want to own a part of history that’s really different,” she said.

Most buyers keep a low profile and many come from outside Germany, she added.

Tom Schimmeck, the radio program’s producer, said that interest in Hitler’s art likely has nothing to do with a societal shift to the right, or a rethinking of Hitler’s crimes. “My impression is it is people who have too much money and want something crazy from Europe,” he said in an interview.

Unlike the buyers, who crave privacy, Weidler’s and other auction houses need to advertise their wares in advance to attract bidders. This can lead to a bizarre relationship with the press, which can be a way to get the word out, but also brings unwelcome questions.

Both Nuremberg and Berlin police were alerted by Droog and his partner Jaap van den Born, both investigative journalists who have made it their mission to stop auctions of Hitler fakes by scouring auction catalogs and alerting local authorities before the sales. They provide police with detailed reports on the paintings, sometimes giving German authorities the crucial information to begin their own investigations.

The comment in the report by Droog and van den Born on “Village on a Mountain Lake” reads: “Yet again a stupid forgery; Hitler didn’t paint lake or mountainscapes.”

By the time the watercolor came up at Weidler’s, most of the audience of 25 or so seemed to be there to watch the spectacle, rather than to bid. Several members of the audience declined to answer when asked why they were there.

None of the five pieces on display that day were sold, but after the auction, a middle-aged man wearing a tailored suit and a hat entered the room and asked discreetly whether the bidding for the Hitler paintings was still going on.

Staff informed him that the auction was over, but that he could make arrangements to see the works in private on Monday.

A week later, the auction house confirmed that it had sold “Village on a Mountain Lake” for 30,000 euros in a private sale.

This article originally appeared in The New York Times.