After Lincoln was assassinated, A.C. Richards swore he was the first to tell Mary about Lincoln’s assassination, and she was not shocked (Kingseed). This suggests that she knew something of that plan. When officials arrived a second time, she acted completely surprised.
Her reaction about this information changed from when Richards told her, to when they came back and told her again.
Apart from her reaction to the news, Mary had a Confederate spy as a son. As a result of having a Confederate son, Mary had many meetings and Confederates in her house. This implies that Mary overheard some of the things that they talked about, therefore knowing about some of their plans. It is proven that John Wilkes Booth did not share his plan with anyone prior to his meeting with his co-conspirators, but Mary may have been involved with the attempted kidnaping of the president. This alone is one move against the president.
Contrarily, Mary’s name was not on the letter Booth wrote (Kingseed). Booth wrote this letter to implicate everyone involved with the murder plot. The names George Atzerodt and Lewis Powell (a.k.a. Paine) were on the letter because they were assigned to kill other members of the Cabinet. He gave this letter to John Matthews, who was supposed to give this letter to the press, but he backed out because he did not want to look as if he was involved. On this letter, Mary’s name was not present. This, however, only proves that she did not participate in the killing of anyone. Alas, she did help Booth by providing binoculars and guns (Kingseed). There is an abundance of information that also proves that she is guilty of supporting Booth.
Mary Surratt had Confederate meetings in her house and she was not surprised about Lincoln's assassination. Because of these examples, Mary Surratt deserved the punishment allotted to her: death by hanging.