Mary Surratt was the first woman executed in the US, on the grounds that she was involved in the conspiracy to assassinate President Lincoln. Whether guilty or innocent, the movie portrays her military trial as unconstitutional. In fact, a year after her execution, the Supreme Court declared that military trials of citizens, even in times of war, were unconstitutional (Ex parte Milligan).
With echoes to John Adams defending the British soldiers involved in the Boston Massacre, Frederick Aiken defends Mary Surratt. Whether the charges were true or not, the justification given for defending her was the constitutional right to representation before the law and to due process. Though in the movie, Aiken initially needed convincing of this justification.
Like many (all?) Northerners immediately following the war, judgment was swiftly passed on Confederates. No trial of one’s peers. No innocent until proven guilty. The need for revenge was enough to condemn. This same prejudice to suspend rights is common enough today.
The movie is a sad look at a time when trials were stacked against people. The Secretary of War Stanton is shown as seeking to defend the country at all costs—even the cost of the Constitution. Some things never change.
Mary Surratt is found guilty and sentenced to hang. Aiken though holds onto the thin hope of a retrial by seeking a writ of habeas corpus, basically claiming that the military trial was unconstitutional. He succeeded in this request, but President Andrew Johnson intervened to deny the writ. And Mary hung with three other conspirators for the assassination of President Lincoln.
The movie, directed by Robert Redford, is well done. The actors give superb performances, especially Robin Wright as Mary Surratt. The situation the movie portrays, just like John Adams defending the British soldiers, challenges us to look not at the guilt or innocence of the accused, but at the rights we legally have enjoyed in the US starting with our status as colonies.
What is the point of striving to preserve the country if we destroy the Constitution in the process? This is the exact opposite stance taken by Secretary of War Stanton and many others that followed in his shoes.