BALTIMORE (AP) — The arrests of a presidential historian and his assistant on charges of stealing documents worth millions from the Maryland Historical Society have other groups nationwide checking the security of their archives.

The Historical Society of Pennsylvania says they have already recovered a letter signed by George Washington that may have disappeared during a visit by the men now charged.

Police found 60 documents at a building being used by the assistant, Jason Savedoff. Many of those had been signed out from historical collections by author Barry Landau.

Landau himself boasts a personal collection of more than a million artifacts. Investigators are taking a closer look at that collection now.

Landau’s attorney rejects the charges. Savedoff’s did not return calls for comment.

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