Source: Benjamin Butler Papers, Manuscript Division, Library of Congress, Washington, D.C.

In 1867 the U.S. House of Representatives established a special committee to investigate the Lincoln assassination. Chaired by Representative Benjamin F. Butler, the committee was largely controlled by Republicans who had become alienated from President Johnson because of his lenient treatment of the defeated South, including his large-scale pardons of Confederate officials.  Butler was one of the most vigorous proponents of Johnson's impeachment during 1867. In November 1867, after the yellow fever epidemic had safely abated, the Butler Committee sent an investigator, William H. Gleason, to Fort Jefferson to interview Dr. Mudd, Spangler, and Arnold. O’Laughlen had died in the epidemic. 

Dr. Mudd, an avid follower of political events in Washington, was well aware of Butler’s efforts to impeach President Johnson, the only person in the world who could free him from Fort Jefferson. Dr. Mudd was not about to do or say anything to alienate the President. He initially refused to give any statement at all to Gleason, but at the urging of the fort’s commander, provided Gleason with the following short declaration. Arnold and Spangler also provided statements to Mr. Gleason, but neither the statements of the three men nor other inquiries made by the Committee shed any new light on the Lincoln assassination. The Committee ceased operation without taking any actions.