Mystery involves documents from Thomas Jefferson, Polish kings, a French emperor and Revolutionary War heroes

The documents — filled with Polish surnames and the signatures of American presidents — started appearing in Harlan J. Berk’s antique shop a few at a time.

It looked like a great buy. After all, it’s not every day that papers with “Jefferson” and “Washington” scrawled on the bottom show up in a Chicago store specializing in old coins. For one set of documents, the young sellers asked for $2,000. Berk’s cashier, so impressed with the collection, paid them twice that.

But Berk’s enthusiasm led to research, and his research touched off an FBI investigation that led to the return of dozens of artifacts stolen decades ago from Chicago’s Polish Museum of America.

Today the artifacts, worth about $5 million, are back home at the museum. The mystery, however, is only partially solved.

Maria Ciesla, the museum’s president, had heard for years about valuable documents that once were part of the collection but hadn’t been seen for decades. Still, it was never clear exactly what was missing or when it disappeared. So when Berk called Ciesla last year to say he had unwittingly bought some of the West Town museum’s property, the museum contacted the FBI, which started an investigation. And then the store owner and museum director also devised a plan.

Berk agreed to keep buying the documents and hand them over to the Polish Museum with the promise that the museum would reimburse him. But the sellers, naive at first, started to “wisen up,” Berk said. They were fascinated with the wax seals of Polish royalty on some papers, and they hinted that they might take those artifacts and some others to a bigger dealer.

Fearing that the remaining lost artifacts would be sold elsewhere, the FBI stepped in. The sellers, who said they found the artifacts in the basement of a home they were renting but knew nothing of their origin, agreed to hand over everything they had.

No one was charged in the disappearance or sale of the documents because of statutes of limitations and the fact that the FBI couldn’t determine who took them or exactly when the artifacts disappeared (they think it was sometime in the 1980s).

In a news release, the FBI said the house in which the artifacts were found was owned by the mother of a former curator of the Polish Museum. Mike Kosanovich, assistant special agent in charge of the FBI’s Chicago office, declined to discuss the curator in greater detail and would not say whether he or she was still alive.

The museum displayed many of the recovered artifacts Wednesday at a joint news conference with the FBI. One letter from former President Thomas Jefferson, written in May 1814 at his Monticello estate in Virginia, discussed the young nation’s banking system and asked for back wages for Revolutionary War hero Thaddeus Kosciuszko, “whose revolutionary services and general devotion to the cause of liberty have rendered him dear to this country.”

In a separate document written in Polish a year later, Kosciuszko discussed what it takes to be a patriotic Pole.

“A citizen who wants to pride himself on being a good Pole should sacrifice everything for his country and always be human and righteous,” he wrote.