 Mount was arrested at Goodspeed's Book Shop in Boston, Massachusetts, on August 13, 1987, by the Federal Bureau of Investigation (FBI) for attempting to sell 158 Civil War documents to Claire Rochefort.These documents had been stolen from the National Archives and Records Administration.Mount was also in possession of additional letters stolen from both the Library of Congress and National Archives, in what is one of the largest rare documents thefts, with the value of the stolen items totalling over $100,000.