(CNN) -- Barry H. Landau is recognized as one of the foremost collectors of presidential artifacts and memorabilia, having worked with every White House since the Lyndon Johnson administration.
Now police in Baltimore are accusing him and another man of stealing millions of dollars worth of historical documents from the Maryland Historical Society.
Landau and Jason Savedoff are accused of stealing documents from the society's museum library after an employee thought the pair exhibited suspicious behavior.
According to a Baltimore Police Department report, the employee said he watched Savedoff take a document, conceal it in a portfolio and walk out of the library with it on Saturday. The employee then called police.
The report states 60 documents were found in Savedoff's locker near the library, some of which were signed out by Landau.
The men were found to be in possession of documents signed by President Abraham Lincoln valued at $300,000, along with signed commemorations of both the Statue of Liberty and the Washington Monument, each valued at $100,000.
The recovered documents also included several presidential inaugural ball invitations and programs with an estimated value of $500,000, according to the police report.
"These are only four (4) of the (60) documents recovered from Mr. Landau and Mr. Savedoff," the police report stated. "The staff of the Maryland Historical Society advised that the other 56 documents are of the same approximate value."
Baltimore police say the FBI has also started an investigation. FBI spokesman Richard Wolf confirmed the joint investigation and said officials are discussing whether the suspects will face both federal and state charges.
The two men are being held in the Baltimore City Detention Center, according to the Maryland Department of Corrections database.
Maryland Historical Society President Burt Kummerow said he is proud of how the museum handled the situation and is pleased the documents have been returned.
"It would have been a huge loss because then (the documents) are no longer in the public record and then they're no longer available," he said.
Dozens of people enter the museum's special collections unit every day to view original artifacts and conduct research.
"We're in business to study the history of Maryland, and that's why people come in," Kummerow said. "But there are others who would love to collect important documents and own them."
Landau is the author of "The President's Table: Two Hundred Years of Dining and Diplomacy."
Earlier this month, he told CNN he has collected more than a million presidential objects. In a July 4 piece, Landau discussed how various presidents displayed the American flag and how aides went about positioning them.
"I would like to be appointed to some national position to assure that there will be a resurgence of the flag pole on every new building, and the American flag more prominently displayed on a day to day basis," Landau said in an interview for the "In The Arena" blog.
CNN's Jay Kernis and Carol Cratty contributed to this report