Story highlights In July, an employee at a Maryland museum spotted a man removing a historial document

Historian Barry Landau and his assistant, Jason Savedoff, were subsequently indicted

They were charged with conspiring to steal historical documents from museums

Savedoff pleaded guilty Thursday, according to federal authorities

A 24-year-old assistant to a presidential historian pleaded guilty Thursday in federal court in Baltimore to conspiring to steal historical documents from museums for hundreds of thousands of dollars in personal profit, according a statement from federal and local authorities in Maryland.

Jason Savedoff, assistant to self-styled presidential historian Barry Landau, admitted to conspiring to steal valuable old documents from museums in Maryland, Pennsylvania, New York and Connecticut, the statement said.

The stolen items include documents signed by Abraham Lincoln, Benjamin Franklin and Franklin D. Roosevelt.

Authorities say the papers signed by Lincoln alone are worth about $300,000, and presidential inaugural ball invitations and programs are believed to be worth $500,000 prosecutors said.

Landau, 63, is an author and frequent television guest as a presidential historian. He claims to have had relationships with several presidents including John F. Kennedy, Richard Nixon, Gerald Ford, and Bill Clinton. He was indicted with Savedoff in July on charges of conspiring to steal historical documents, and he is awaiting trial

Savedoff signed a plea agreement that said he had stolen the documents and manuscripts from December 2010 through July 2011, the statement from federal authorities -- including Rod J. Rosenstein, U.S. attorney for Maryland, and Baltimore Police Commissioner Frederick H. Bealefeld III -- said.

Savedoff admitted that he and his co-conspirator prepared lists containing the names of historical figures and the estimated value of the signatures and documents before they were taken from the museums, the statement said.

He was spotted removing a document from a Maryland museum by an employee. The two men were arrested in July.

Savedoff could receive up to five years in prison for the conspiracy and 10 years for the theft. He is scheduled to be sentenced February 10.