Surratt was then tried along with Payne, Mudd, Arnold and Spangler and three others (David Herold, George Atzerodt, and Michael O'Laughlin). And government agents generally concluded that the conspirators used Surratt's house as a headquarters or meeting-place. Thus, her supposed complete lack of knowledge of their various plans seemed implausible.
For a brief period of time, Mary and her fellow prisoners were kept on board two ironclad warships and in solitary confinement. With the exception of Mary, each was forced to wear a canvass hood with a single hole provided for breathing and eating. Guards were instructed to have (and allow) no conversation with the prisoners. Surratt, on the other hand, was allowed visits from her daughter and two catholic priests. The prisoners were then transferred to the Old Capital Prison before going to the Old Penitentiary Building on the grounds of the Washington Arsenal.
As the trial got under way, tight fitting hoods made of inch-thick cotton replaced the canvass coverings. In the courtroom, most of the prisoners were laden with steel anklets and heavy iron weights. Their hands were also fastened to heavy, ten-inch-long iron bars. Guards were placed between each prisoner. The distinguished Dr. Mudd wore only ordinary handcuffs. Mary Surratt was generally free of restraint.
on or before the 6th day of March, A.D. 1865, and on divers other days and times between that day and the 20th day of April, A.D. 1865, [did] receive, entertain, harbor, and conceal, aid and assist [the] confederates, with the knowledge of the murderous and traitorous conspiracy [and] with intent to aid, abet, and assist them in the execution thereof, and in escaping from justice after the murder [of] Abraham LincolnJudge Advocate General Joseph Holt and his assistants steered case throughout the six-week trial. Over four hundred and fifty witnesses were subpoenaed and there were three hundred and sixty-one appearances on the stand. The testimony took up four thousand pages and the arguments of the lawyer accounted for another seven hundred.
Witnesses clearly placed various conspirators in Mary Surratt's home, but none demonstrated or even professed that she had knowledge of the assassination. Louis Weichmann, a former fellow student of Mary's husband (John) at St. Charles College, testified that Surratt would "sometimes" hold private conversations with Booth. He also said Booth once gave him ten dollars to hire a carriage for Mrs. Surratt. But, after the trial, Weichmann claimed he exchanged testimony for the promise of a job!
John Lloyd, a former policeman turned tavern-keeper (and frequent user), was also called to testify against Surratt. The widow's husband had once asked Lloyd to store (hide) two army carbines, ammunition, rope and a monkey wrench. On April 11, Lloyd passed by Surratt and Weichmann on a country road. Surratt supposedly asked Lloyd to get the "shooting irons" out and have them ready since they would be "wanted soon." Weichmann, sitting right next to Surratt, could neither confirm nor deny such words were spoken. Lloyd also claimed that, on Good Friday, Surratt again reminded him to have guns ready. Lloyd had been drinking heavily that day, but was confident of the exact content of the conversation, even more so than he was about the content of the earlier conversation along the roadside. Long after the trial, he would make the astounding claim that he was forced to testify against Surratt under the threat of death!
The military judges deliberated for two days. Death sentences were given to David Herold, George Atzerodt and Lewis Paine. Dr. Samuel Mudd, Samuel Arnold and Michael O'Laughlin were sentenced to life imprisonment. Edward Spangler was given a six-year sentence.
Author Francis X. Busch concludes Surratt would, "in all likelihood," have been "promptly acquitted" before an "honestly selected jury" in a civil court. More pointedly, author John Cottrell agrees that no civil court would have convicted Surratt on the "unsupported evidence of a drunkard" (Lloyd).
Later, one of the Military Commission's members, General David Hunter, supposedly reported that the first vote actually resulted in a life sentence for Mary Surratt. But Judge Advocate General Holt and Assistant Judge Advocate Bingham conducted a re-reading of the testimony and pressed for the death sentence with a recommendation to the President for mercy. So, the Commission recommended death and five of its nine members (General Robert S. Foster, Colonel C.H. Tompkins, Major General David Hunter, General A.V. Kautz and General James A Ekin) signed a plea for clemency. It read:
To the President: The undersigned, members of the military commission appointed to try the persons charged with the murder of Abraham Lincoln, etc., respectfully represent that the Commission have been constrained to find Mary E. Surratt guilty upon the testimony of the assassination of Abraham Lincoln, late President of the United States, and to pronounce upon her, as required by law, the sentence of death; but in consideration of her age and sex, the undersigned pray your Excellency, if it is consistent with your sense of duty, to commute her sentence to imprisonment for life in the penitentiary.
But, at the moment, the most sensational story was that of Anna Surratt, Mary's sister. Anna attempted to visit the President herself on July 7, but was prevented from doing so by various officials. Newspapers could not resist describing her trauma and desperate act in elaborate detail. The widow of Stephen A. Douglas also attempted to persuade Johnson to save Surratt from the gallows.
On the day of the execution, the prisoner's were marched to the scaffold at bayonet point. Famed photographer Mathew Brady was given permission to record the scene. Harper's Weekly sent two artists. Surratt was shielded from the sun and ninety-two degrees by an umbrella as she ascended the thirteen steps. Authors Brandt Aymar and Edward Sagarin suggest Surratt "expected intervention" from the President "until the moment that she stepped upon the scaffold."
It must have been more than Surratt's soul could bear to hear Louis Paine's last words. He protested that she was innocent. It is reported that the last words of the first woman ever executed by the United States Government were, “Don’t let me fall.”