A Roman Catholic,Weichmann entered St. Charles College when he was sixteen with the intention of becoming a priest. While at the college in Maryland he met John Surratt. Both men decided to abandon their plans of entering the church and moved to Washington where Weichmann found work as a schoolteacher.
Soon after the start of the American Civil War Weichmann went to work as a clerk in the rapidly expanding War Department. In November, 1864, Weichmann became a lodger at the boarding house owned by Mary Surratt, the mother of John Surratt. This brought Weichmann into contact with other friends of the family including John Wilkes Booth.
After the assassination of Abraham Lincoln, Weichmann, as an associate of John Wilkes Booth, was arrested and threatened with being charged with the crime. Later it was claimed that Weichmann was offered a deal and that in return for his testimony in court, he would be allowed to go free.
At the trial John M. Lloyd told the court that on the Tuesday before the assassination Weichmann and Mary Surratt visited him. Lloyd claimed that Mrs. Surratt "told me to have those shooting-irons ready that night, there would be some parties who would call for them. She gave me something wrapped in a piece of paper, which I took up stairs, and found to be a field-glass. She told me to get two bottles of whisky ready, and that these things were to be called for that night."
When Weichmann testified he claimed he could not hear what Mary Surratt said to John M. Lloyd as they spoke in hushed tones. He did tell the court that he had seen John Wilkes Booth, Lewis Powell, George Atzerodt and David Herold in Mrs. Surratt's house together. This supported the prosecution's claim that the boarding house was where the assassination plot had been planned.
Weichmann also testified that he was with John Wilkes Booth in Washington on 23rd December when he had met Samuel Mudd, another man charged with conspiring to assassinate Abraham Lincoln. This was important evidence as Mudd denied that he had met Booth in Washington.
On 29th June, 1865, Mary Surratt, Lewis Powell, George Atzerodt and David Herold were also found guilty of the conspiracy to murder Abraham Lincoln and were hanged at Washington Penitentiary eight days later. It has been argued by historians that Weichmann's testimony in court had been crucial in the conviction of Mrs. Surrett.
After the trial Edwin M. Stanton, the Secretary of War, and Joseph Holt, the government prosecutor, helped get Weichmann the post as clerk of the Philadelphia Custom House. Weichmann lost the job in November, 1866, when President Andrew Johnson decided to purge people that held jobs obtained via the Republican Party.
When Ulysses Grant became president, Edwin M. Stanton arranged for Weichmann to get his job back with the Philadelphia Custom House. When Grover Cleveland and the Democratic Party came to power in 1886, Weichmann was sacked again. He now moved to Indiana where he established the Anderson Business College. Louis Weichmann died in 1902.
On Friday, the day of the assassination, I went to Howard’s stable, about half-past 2 o’clock, having been sent there by Mrs. Surratt for the purpose of hiring a buggy. I drove her to Surrattsville the same day, arriving there about half-past 4. We stopped at the house of Mr. Lloyd, who keeps a tavern there. Mrs. Surratt went into the parlor. I remained outside a portion of the time, and went into the bar-room a part of the time, until Mrs. Surratt sent for me. We left about half-past 6. Surrattsville is about a two-hour drive to the city, and is about ten miles from the Navy Yard bridge. Just before leaving the city, as I was going to the door, I saw Mr. Booth in the parlor, and Mrs. Surratt was speaking with him. They were alone.
Some time in March last, I think, a man calling himself Wood came to Mrs. Surratt’s and inquired for John H. Surratt. I went to the door and told him Mr. Surratt was not at home; he thereupon expressed a desire to see Mrs. Surratt, and I introduced him, having first asked his name. That is the man (pointing to Lewis Powell). He stopped at the house all night. He had supper served up to him in my room; I took it to him from the kitchen. He brought no baggage; he had a black overcoat on, a black dress-coat, and gray pants. He remained till the next morning, leaving by the earliest train for Baltimore. About three weeks afterward he called again, and I again went to the door. I had forgotten his name, and, asking him, he gave the name of Powell I ushered him into the parlor, where were Mrs. Surratt, Miss Surratt, and Miss Honora Fitzpatrick. He remained three days that time. He represented himself as a Baptist preacher; and said that he had been in prison for about a week; that he had taken the oath of allegiance, and was now going to become and good and loyal citizen. Mrs. Surratt and her family are Catholics. John H. Surratt is a Catholic, and was a student of divinity at the same college as myself. I heard no explanation given why a Baptist preacher should seek hospitality at Mrs. Surratt’s; they only looked upon it as odd, and laughed at it. Mrs. Surratt herself remarked that he was a great looking Baptist preacher.
I met the prisoner, David E. Herold, at Mrs. Surratt’s on one occasion; I also met him when we visited the theater when Booth played Pescara; and I met him at Mrs. Surratt’s, in the country, in the spring of 1863, when I first made Mrs. Surratt’s acquaintance. I met him again in the summer of 1864, at Piscataway Church. These are the only times, to my recollection, I ever met him. I do not know either of the prisoners, Arnold or O’Laughlin.
I proclaim it here and before the world that Louis J. Weichmann was a party to the plan to abduct President Lincoln. He had been told all about it, and was constantly importuning me to let him become an active member. I refused, for the simple reason that I told him that he could neither ride a horse nor shoot a pistol, which was a fact.
I have very little to say of Louis J. Weichmann. But I do pronounce him a base-born perjurer; a murderer of the meanest hue! Give me a man who can strike his victim dead, but save me from a man who, through perjury, will cause the death of an innocent person. Double murderer!!!! Hell possesses no worse fiend than a character of that kind. Away with such a character. I leave him in the pit of infamy, which he has dug for himself, a prey to the lights of his guilty conscience.