Investigators are probing whether a prominent historian and an associate accused of stealing valuable documents from the Maryland Historical Society also took papers from the National Archives and a handful of other libraries, a prosecutor said in court Tuesday.

The revelation came as a Baltimore City Circuit Judge set bail for Barry H. Landau, 63, at $500,000 and Jason Savedoff, 24, at $750,000. The pair were charged earlier this month with taking 60 historic documents. The papers included some signed by Abraham Lincoln, inaugural ball invitations and a commemoration of the Washington Monument, according to court documents.

On July 9, Landau and Savedoff were arrested after an employee at the Baltimore archive saw Savedoff slip a document in a portfolio and walk out of the library, according to court documents. Police later found 60 documents stashed in Savedoff’s laptop bag in a locker, according to court documents. Landau had signed the documents out, authorities said....