SEATTLE — An 18-carat gold bookmark reportedly owned by Adolf Hitler and stolen from an auction house in Spain six years ago has been recovered by American authorities in an undercover operation halfway around the world.

Christian Popescu, a Romanian national, was arrested Tuesday outside a Bellevue Starbucks after trying to sell the bookmark to an undercover agent for $100,000, according to papers filed in U.S. District Court.

Federal prosecutors said the bookmark was among several items taken in an auction-house heist in Madrid, Spain, six years ago. At the time, some antiquities experts questioned its authenticity.

The bookmark was reportedly given to Hitler by his longtime mistress, Eva Braun, to console him after German forces surrendered at Stalingrad. The bookmark is engraved with a portrait of Hitler as well as an imperial eagle and swastika.

“My Adolf, don’t worry,” it reads, adding that the loss was “only an inconvenience that will not break your certainty of victory. My love for you will be eternal, as our Reich will be eternal. Always yours, Eva. 3-2-43.”

Regardless of its authenticity, federal agents said its theft broke the law.

“Artifacts of historical significance are not souvenirs for illegal sale to the highest bidder,” Leigh Winchell, special agent in charge of Immigration and Customs Enforcement’s office of investigations in Seattle, said in a statement.

Popescu made an initial appearance in federal court Wednesday, where he was represented by a public defender who left without speaking to reporters.

A man who described himself as Popescu’s roommate called the undercover operation a “setup.”

“I don’t think Christian is involved in anything. He doesn’t have any prior record. He’s a business owner, a clean person,” the man, Kleon Tona, said outside the courthouse. “We came over as normal people. Just looking for a better life, not a life to do things like this. I think it’s a big setup.”

Tona said Popescu immigrated to the Seattle area about 12 years ago.

Popescu is being held on one count of sale or receipt of stolen goods. A detention hearing was set for Monday.

According to charging papers, ICE learned in August that Popescu was trying to sell the bookmark in the Seattle area. Through an informant, agents learned that Popescu had shopped the bookmark in the area three years ago, and would pay a 10 percent commission if the informant could find a buyer.

The informant helped arrange the sale to an undercover agent, the papers said. Popescu allegedly wanted $150,000 for the bookmark, but settled for $100,000.

Spanish authorities estimated its value at $13,000 to $17,000, court documents say.

U.S. Attorney Jeff Sullivan said agents are still investigating how the bookmark arrived in Seattle. Five people were detained in Tuesday’s operation, but only Popescu was arrested and charged, he said.

In 2002, three thieves — described as Eastern European — walked into the Duran Subastas auction house in Madrid during work hours and stole the bookmark along with several pieces of jewelry from a showcase.

The bookmark’s owner at the time was described as Brazilian.