In the turmoil that followed the assassination od president Abraham Lincoln , scores of suspected accomplices were arrested and thrown into prison. All the people who were discovered to have had anything to do with the assassination or anyone with the slightest contact with Booth or Herold on their flight were put behind bars. Among the imprisoned were Louis J. Weichmann, a boarder in Mrs. Surratt’s house; Booth’s brother Junius (playing in Cincinnati at the time of the assassination); theatre owner John T. Ford, who was incarcerated for 40 days; James Pumphrey, the Washington livery stable owner from whom Booth hired his horse; John M. Lloyd, the innkeeper who rented Mrs. Surratt’s Maryland tavern and gave Booth and Herold carbines, rope, and whiskey the night of April 14; and Samuel Cox and Thomas A. Jones, who helped Booth and Herold escape across the Potomac.
All of those listed above and more were rounded up, imprisoned, and released. Ultimately, the suspects were narrowed down to just eight prisoners (seven men and one woman)Samuel Arnold, George Atzerodt, David Herold, Samuel Mudd, Michael O’Laughlen, Lewis Powell, Edmund Spangler (a Ford’s stagehand who had given Booth’s horse to “Peanuts” Burroughs to hold), andMary Surratt.
The eight suspects were tried by a military tribunal ordered by then-President Andrew Johnson on May 1, 1865. The nine-member commission was presided over by Major General David Hunter. The other eight voting members were Major General Lew Wallace, Brigadier Generals Robert Sanford Foster, Thomas Maley Harris, Albion P. Howe, and August Kautz, Colonels James A. Ekin and Charles H. Tompkins, and Lieutenant Colonel David Ramsay Clendenin. The prosecution team was led by U.S. Army Judge Advocate General Joseph Holt, assisted by Congressman John A. Bingham andMajor Henry Lawrence Burnett. The transcript of the trial was recorded by Benn Pitman and several assistants, and was published in 1865.
The fact that they were tried by a military tribunal provoked criticism from both Edward Bates and Gideon Welles, who believed that a civil court should have presided. Attorney General James Speed, on the other hand, justified the use of a military tribunal on grounds that included the military nature of the conspiracy, that the defendants acted as enemy combatants and the existence of martial lawin the District of Columbia. (In 1866, in the Ex parte Milligan decision, the United States Supreme Court banned the use of military tribunals in places where civil courts were operational.)The odds were further stacked against the defendants by rules that required only a simple majority of the officer jury for a guilty verdict and a two-thirds majority for a death sentence. Nor could the defendants appeal to anyone other than President Johnson.
The trial lasted for about seven weeks, with 366 witnesses testifying. Louis Weichmann, released from custody, was a key witness. All of the defendants were found guilty on June 30. Mary Surratt, Lewis Powell, David Herold, and George Atzerodt were sentenced to death by hanging; Samuel Mudd, Samuel Arnold, and Michael O’Laughlen were sentenced to life in prison. Mudd escaped execution by a single vote, the tribunal having voted 5–4 against hanging him. Edmund Spangler was sentenced to imprisonment for six years. Oddly, after sentencing Mary Surratt to hang, five of the jurors signed a letter recommending clemency, but Johnson refused to stop the execution. (Johnson later claimed he never saw the letter.)
Surratt, Powell, Herold, and Atzerodt were hanged in the Old Arsenal Penitentiary on July 7, 1865. The executions were supervised by Union general Winfield Scott Hancock. Mary Surratt was the first woman executed by the United States government.O’Laughlen died in prison of yellow fever in 1867. Mudd, Arnold, and Spangler were pardoned in February 1869 by President Johnson. Spangler, who died in 1875, insisted for the rest of his life that he had no connection to the plot beyond being the man Booth asked to hold his horse.