I was introduced to Jimmy—I never learned his surname—during a visit to Athens in 2005. I was told that he had dozens of artworks, all of which he wanted to sell, but he wanted it to be utterly confidential. It seemed unlikely, but as I’ve learned from years in the business, it’s important to follow every lead; you never know where the next deal will come from. I was driven to Jimmy’s house in the suburbs of Athens. The gate opened, and at the end of the driveway, in gray sweats, stood Jimmy, puffing on a cigar. After insisting on complete discretion, he let me in.

The first thing I saw was a Cézanne landscape.

“You own this Cézanne?,” I asked. Jimmy just nodded. This was incongruous, to say the least. Here we were in suburban Athens, and a very tanned man in sweatpants had a museum-quality painting on his wall. It was easily worth $10 million. The picture next to it was an intricate Van Gogh on paper, and as I looked around, I saw more works by Impressionist and Post-Impressionist masters.

He had two Tahitian Gauguins, an early Picasso, an early figurative Kandinsky from his Murnau period, a wonderful Matisse drawing of his studio with the fishbowl. And so it went on. I was exhausted from marveling at all this stuff.

From Jimmy’s collection: a self-portrait on paper by Vincent van Gogh.

“You want to sell some of this?,” I asked.

“Yes, but I have a problem,” replied Jimmy.

He told me to turn the Cézanne around. I took it off the wall and turned it around, and there, on the back, imprinted on the canvas, was a small, round stamp. It had three elements—the year 1943, an eagle, and two letters, in a stylized font, that made them look like lightning bolts: SS.

I looked up at Jimmy. He just nodded, with such a guilty and shameful look that I thought he’d start crying. I looked at it again. There was no mistake. This was the stamp of the SS, the Nazi Schutzstaffel. It had been put there by a member of the Third Reich. I felt lightheaded. This was Jimmy’s problem.

I tried to reassure him. “It’s O.K. There’s always an answer.” But that didn’t lift his mood. “Turn around the Van Gogh,” he said. I did, and there was another “SS.”

“Oh my God, Jimmy. Another one?,” I said. “This is not good. How many of your pictures have this?”

“All of them,” he said sadly.

I knew about looted paintings, and occasionally I’d been offered work that was of questionable provenance. But I’d never seen a painting with such incontrovertible evidence of its having been stolen by the Nazis, let alone an entire collection.

“Let me show you something else,” said Jimmy.

He brought over a beautiful Degas oil. It was a small painting of a bather, with vibrant colors melting into each other. I turned it around, and on the back, in large script handwriting, were the words “Das Bild gehört meiner Sammlung am.” (The painting belongs to my collection).

Underneath it was written the word “Kollektor” (collector) and the name “H. Göring.” There was a Reichsadler stamp depicting an eagle holding a Nazi swastika.

From Jimmy’s collection: The inscription on the back of a Degas oil painting, identified it as once having belonged to the infamous, looted art collection of Hermann Göring, Hitler’s right-hand man.

I started looking at all the other pictures—Monets, Renoirs, more Van Gogh drawings, a Toulouse-Lautrec painting on board. The entire canon of late-19th- and early-20th-century art was represented, and all—literally all—had either an “SS” stamp, a Reichsadler stamp, or an inscription on the back showing that they had been looted.

Jimmy explained that years ago he had made a huge oil deal with the government of Yugoslavia. When it came time to pay him, the Yugoslav government was unable to come up with the funds. As a trade-off, Jimmy was offered three huge crates full of pictures. He said he had no knowledge of art—and no alternative—so he took them.

Jimmy had held on to this secret for almost 20 years, and I could tell the toll of keeping it had been terrible. But now he was on a roll. He disappeared and came back with other Nazi-tainted works. “Here, tell me who this is,” he would say, covering the signature. “Picasso,” I would answer, or “Manet,” or “Kirchner.” It was all so obvious. But when he appeared with a small landscape on paper, I was stumped.

“Pissarro?,” I guessed. “No. Sisley!”

When Jimmy moved his hand away from the signature, the name burned itself onto my retina: “Hitler.”

From Jimmy’s collection: left, a watercolor by Toulouse-Lautrec; right, a gouache on paper by Henri Matisse.

That wasn’t all. He had a paint kit that had belonged to Van Gogh and an entire notebook of drawings by Toulouse-Lautrec. It’s long been rumored that one of Toulouse-Lautrec’s notebooks is missing. Now, seemingly, here it was in my hands. By the time we were done, about four hours had passed. I was swimming in a waking fever dream of beauty and horror.

Jimmy was ready to let all of this go—it seemed it would be a relief for him—and I suspected that if I came to him with a cash offer of a fraction of the value, he would jump at it. But buying it was only half the challenge. How was I to dispose of it?

In general, the Nazis stole from two groups: families, usually Jewish ones; and German and Austrian state museums, which they looted in the hope of erasing any so-called degenerate art. I figured that if I could get the paintings for the right price, I would immediately return all the works that were stolen from collectors and their families. But the works that were looted from German and Austrian museums would belong to me and my gallery. If those murderous bastards had been stupid enough to loot themselves, then too bad.

I needed advice on how to do this, so I called Randol Schoenberg, the Los Angeles lawyer who had helped retrieve the plundered Portrait of Adele Bloch-Bauer, by Gustav Klimt, which is now the jewel of the Neue Galerie in New York. Randy was immediately interested in the case and agreed that I should get the works authenticated by the pertinent experts: Wanda de Guébriant for Matisse, Vivian Barnett for Kandinsky, the Comité Marc Chagall, the Toulouse-Lautrec committee, the Van Gogh Museum, in Amsterdam. I e-mailed high-resolution photos of the respective pictures to each one. I told them about the Nazi stamps on the back and explained that I wanted to make sure this was all done properly.

From Jimmy’s collection: Top, the front of the painting shows a version of Van Gogh’s Wheatfield with Crows on panel. Van Gogh often utilized wooden panels, particularly for smaller works and studies. Above, the back shows a Reichsadler stamp overlaid with a signature that appears to be that of Göring.

I waited on tenterhooks for the next few days. The first reply came from de Guébriant. “Fake!” she declared. “An outright fake!” Next came Barnett, who was gentler: “Not by Kandinsky.” The opinions flowed back. All the artworks were fake.

I’ve been around long enough to know that even the best collections have fakes—there are fakes in many world-class museums. (I have stories about that, too.) But while I suspected some of the pictures in Jimmy’s collection might be forgeries, I didn’t think all of them would be.

With Jimmy’s pictures, my doubts kept being tempered by the details. Art dealers know the back of a painting is more important than its front. The back is where you trace the painting’s history, and the clues for each artwork in Jimmy’s collection were incredible, including incidental marks and labels on each painting, not to mention all those Nazi stamps.

I called Randy, and he was shocked. He had consulted his own expert, who thought the paintings were genuine. I couldn’t help but wonder whether Jimmy had a hand in orchestrating all of it or was just an unwitting patsy. When I called him to tell him the paintings were fakes, he simply got quiet, then in a very low, gravelly voice, he said, “I’m sorry, Ezra.”

From Jimmy’s collection: a drawing by Paul Klee.

Had they been real Nazi loot, I would have felt obligated to inform Interpol. But these were fakes, which rendered them radioactive to an art dealer. The last thing I wanted at that time was a scandal, so I washed my hands of Jimmy. (My own scandal—being busted for wire fraud—would happen much later.)

What I didn’t realize, until last month, was that Jimmy’s collection wasn’t a one-off.

A Bright and Shiny Flaw

While writing up Jimmy’s story, I contacted Raymond Dowd, who has handled some of the most important and successful legal cases regarding the restitution of Nazi art. I wanted to see if he had heard of fake Nazi stamps on fake looted art before. He hadn’t, but he drew my attention to Wolfgang Beltracchi, whose Max Ernst forgery was so good it had been authenticated by Werner Spies, director of the Centre Pompidou and the worldwide authority on Ernst at the time, and sold for $7 million in 2006. (When it comes to fakes, no one’s infallible.)

One of the techniques Beltracchi used was to apply labels to the backs of some of his canvases to make the artworks look as if they had once belonged to the celebrated Jewish-German collector Alfred Flechtheim. In Dowd’s view, the fake Flechtheim labels, as well as the bogus Nazi stamps on Jimmy’s works, served as a form of misdirection: you show a potential buyer something with a bright and shiny flaw—they’d been looted—in order to avert their attention from the bigger issue of whether or not the work is real.

However, when I spoke to the journalist and art expert Stefan Koldehoff, who helped break the news of Beltracchi’s scam, in 2010, he told me a story that gave me shivers. In 2003, he recalled, a Greek woman in Athens named Doreta Peppa announced she had a huge trove of Cézannes and Van Goghs. All of the paintings were marked with “SS” stamps and other Nazi insignia.

While Jimmy’s collection purportedly came from Yugoslavia, Peppa claimed that her father, an officer in the Greek Resistance, had obtained the paintings during the Second World War when the Germans put thousands of plundered artworks onto a train they sent to Greece for safekeeping.

Art dealers have to be cynical, and now questions flooded my mind: Did Peppa know Jimmy? Had she sold her bogus art to him, or vice versa? Or was she in cahoots with him?

However, when I tracked her down and called her, I was quickly cognizant that she was not a fraudster. It was worse than that—she was a believer. She had spent much of her life and fortune hiring forensic labs to verify the pictures (they failed to), contacting art experts (they ignored her), and even writing to Queen Elizabeth II to inform her that the lost Portrait of Dr. Gachet, by Van Gogh, was not in Buckingham Palace (as some art conspiracists believe to be the case) but in Peppa’s own collection.

She sent me more than two decades’ worth of documents charting her quest to get the artworks authenticated. She genuinely believed that she had in her possession objects that would change her life and even contribute to art history in some way. However, for years she had been dismissed as a crackpot. It didn’t help that she was a self-professed high priestess of a religion that worshipped the ancient Greek gods.

Doreta Peppa holds up a scanned copy of a Van Gogh drawing from her collection, 2008.

“I don’t know of any Jimmy,” she tells me when I ask about him, but she was happy to share images of her collection with me. They were from the same era as Jimmy’s, but they were not the same pictures. Neither were they as convincing. It seemed like Peppa had fallen victim to the most insidious condition that afflicts all members of the art world—the insistent belief in the wildest stories.

My theory is that all the Nazi-stamped art came from the same place. It feels like Jimmy’s collection was painstakingly generated by an unknown Greek forger who aimed to create a massive deception. But it took a while for the forger to get good at his craft, or there were some paintings left over, and that was what ended up in Peppa’s collection. But why did the forger think having Nazi stamps on the back would help sell them?

Randy had thought the Nazi stamps on the back of the paintings had been placed there to give the fake works “macabre believability” and to prevent buyers from getting the paintings authenticated by experts, for fear of being denounced as owning looted art. Indeed, an owner of obvious Nazi loot would be reluctant to show it to anyone. This had seemingly been the case with Jimmy for almost 20 years, until he simply couldn’t keep the secret any longer.

But Dowd thought the reason was a little more unsettling. The Nazi stamps gave the paintings a morbid allure: “Baked into ownership of forbidden goods is the possibility that it could get you in trouble,” he says. “That’s the point of pride, the lack of legality makes them sexy, makes them interesting. That’s the attraction.”

He went on: “People who are contemporaries of that era tell me Americans went to Paris after World War II, and they would tell the gallery owner, ‘No, no, no. Show me what’s in the back room that nobody gets to see, and I want it.’ And they knew it was fucking stolen. That was the sport.”

In my years of meeting collectors, I’ve realized that many prefer the forbidden fruit. In its own perverse way, it just tastes a little sweeter. But beware: your perverse fascination with forbidden provenance—the back of the canvas—may keep you from examining a painting’s more obvious faults on the front.

Ezra Chowaiki is writing a book, and working on a documentary, about his experiences in the art world