In 1862, a year after the outbreak of the American Civil War, both Weichmann and Surratt left the seminary without becoming priests. Weichmann went to Washington, D.C., where he taught school for two years at St. Matthew's Institute for Boys. After leaving this position in 1864, he became a clerk in the Department of War, headed by Secretary Edwin Stanton. Surratt had in the meantime become a courier and agent for the Confederacy, working out of Union territory. As a result of his earlier friendship with Surratt, Weichmann took lodgings in the boarding house of Surratt's mother, Mary Surratt, in Washington, D.C. This brought him into contact with the major conspirators involved in Abraham Lincoln's assassination. According to Weichmann's testimony at the trial of the conspirators, John Wilkes Booth, David Herold, Lewis Payne, George Atzerodt, John Surratt, and others continually met at Mary Surratt's boarding house prior to the assassination.