(CNN) -- A self-styled historian who claimed to have moved among presidential circles is expected to be sentenced Monday after he pleaded guilty to stealing historical documents worth well over a million dollars.
Barry Landau, 63, of New York admitted guilt in a Baltimore federal court in February to charges of conspiracy and theft of historical documents.
Prosecutors said he stole from museums in Maryland, New York, Pennsylvania and Connecticut.
After Landau was arrested in July, a search of his New York home turned up more than 10,000 documents.
More than 4,000 have been traced to items taken from libraries and repositories.
The documents include signatures of George Washington, John Adams, Abraham Lincoln and Franklin Roosevelt.
Other documents were signed by Marie Antoinette, Napoleon Bonaparte, Karl Marx and Sir Isaac Newton.
Laundau and a young researcher, Jason Savedoff, 24, admitted visiting numerous museums with the intent to steal valuable documents during 2010 and 2011.
They posed as researchers to access collections they deemed valuable, and then used various techniques to steal them, prosecutors said.
"These techniques included concealing documents inside sports coats and other outerwear which had been modified to contain hidden pockets, as well as distracting museum curators to disguise their actions," the U.S. Attorney's Office in Maryland said.
The pair made sure they also stole the card catalogue entries for the items so museums would not discover they were missing, authorities said.
From the Franklin D. Roosevelt Presidential Library in New York's Hyde Park, the pair stole seven "reading copies" of speeches the president delivered, the U.S. Attorney's Office said.
"Reading copies" are the copies of the speeches from which Roosevelt read, and contain edits he made and his signature.
Landau sold four of these copies to a collector in December 2010 for $35,000, authorities said.
The pair was arrested in July 2011, after a suspicious curator saw Savedoff stash a document into his portfolio in the Maryland Historical Society in Baltimore.
Savedoff has pleaded guilty to the same charges as Landau.
Officials say they could receive prison terms of five years for the conspiracy; and 10 years in prison for theft of the documents.
Authorities say Landau may have dined at the White House and perhaps met past presidents, but they believe many of his stories may not be true.
Experts who have checked records found Landau, at best, had exaggerated his supposed relationship with past presidents. He had appeared on several news outlets, including CNN, as a self-proclaimed presidential historian.
A Washington Post account in July quoted sources who questioned Landau's various claims of relationships with the high and mighty in government circles over some 20 years.