PHILADELPHIA (CBS) — Two rare documents are back where they belong after FBI agents tell Eyewitness News someone stole them from Girard College.

The two documents went missing sometime between 1965 and 2006, according to authorities with the FBI Art Crime Team in Philadelphia.

The documents belong to the Stephen Girard Collection at Girard College. Girard was once the wealthiest man in America. The FBI and U.S. Attorney in Philadelphia took the case, and recovered the 1809 and 1811 journals written by H.J. Roberjot, Girard’s right hand man. They include important glimpses into the millionaire’s life.

“The Girard collection is one of the most important collections in early American history,” Librarian Patrick Spero with the American Philosophical Society told Eyewitness News.

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Spero says his office got a phone call from a rare bookseller in Maine who wanted to sell the two documents. The documents were never supposed to leave Girard College in Philadelphia. “Any missing piece really harms the potential of this collection to help us understand our own past,” Spero told Eyewitness News.

After months of preparation, FBI agents were ready to return the documents. They invited us to come along, as they made the trip to Girard College.

FBI Special Agent Jake Archer with the FBI Art Crime Team worked on the case and presented the documents to Girard College President Clarence Armbrister. “I was surprised quite frankly to know that some of our documents got out of the safekeeping here at Girard College,” Armbrister told Eyewitness News.

Someone stole the documents, and FBI agents, citing internal evidence, believe it was between 1965 and 2006. Authorities may never know who or why but they do know the rare documents are back where they belong.

“It’s a wonderful occasion to reunite these primary source documents with the Stephen Girard archives,” Archer told Eyewitness News.

FBI Special Agent Tim Carpenter heads up the Art Crime Team in Washington, D.C. and made the trip to Girard to personally see the handover.

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“When institutions suffer a theft like this the theft of the object usually becomes part of the life story of that object,” Carpenter told Eyewitness News.