Their agreement and co-operation in the common object having been thus established, the letter written to Booth by the prisoner Arnold, dated March 27, 1865, the handwriting of which is proved before the court, and which was found in Booth's possession after the assassination, becomes testimony against O'Laughlin, as well as against the writer Arnold, because it is an act done in furtherance of their combination. That letter is as follows:—

"Dear John:—Was business so important that you could not remain in Baltimore till I saw you? I came in as soon as I could, but found you had gone to Washington. I called also, to see Mike, but learned from his mother he had gone out with you and had not returned. I concluded, therefore, he had gone with you. How inconsiderate you have been! When I left you, you stated that we would not meet in a month or so, and therefore I made application for employment, an answer to which I shall receive during the week. I told my parents I had ceased with you. Can I, then, under existing circumstances, act as you request? You know full well that the government suspicions something is going on there, therefore the undertaking is becoming more complicated. Why not, for the present, desist?—for various reasons, which, if you look into, you can readily see without my making any mention thereof. You, nor any one, can censure me for my present course. You have been its cause, for how can I now come after telling them I had left you? Suspicion rests upon me now from my whole family, and even parties in the country. I will be compelled to leave home any how, and how soon I care not. None, no, not one, were more in favor of the enterprise than myself, and to-day would be there had you not done as you have. By this I mean manner of proceeding. I am, as you well know, in need. I am, you may say, in rags, whereas, to-day, I ought to be well clothed. I do not feel right stalking about with means, and more from appearances a beggar. I feel my dependence. But even all this would have been, and was, forgotten, for I was one with you. Time more propitious will arrive yet. Do not act rashly or in haste. I would prefer your first query, 'Go and see how it will be taken in Richmond,' and ere long I shall be better prepared to again be with you. I dislike writing. Would sooner verbally make known my views. Yet your now waiting causes me thus to proceed. Do not in anger peruse this. Weigh all I have said, and, as a rational man and a friend, you cannot censure or upbraid my conduct. I sincerely trust this, nor aught else that shall or may occur, will ever be an obstacle to obliterate our former friendship and attachment. Write me to Baltimore, as I expect to be in about Wednesday or Thursday; or, if you can possibly come on, I will Tuesday meet you at Baltimore at B.

"Ever I subscribe myself, your friend,
"Sam."

Here is the confession of the prisoner Arnold, that he was one with Booth in this conspiracy; the further confession that they are suspected by the government of their country, and the acknowledgment that since they parted Booth had communicated, among other things, a suggestion which leads to the remark in this letter, "I would prefer your first query, 'Go and see how it will be taken at Richmond,' and ere long I shall be better prepared to again be with you." This is a declaration that affects Arnold, Booth, and O'Laughlin alike, if the court are satisfied, and it is difficult to see how they can have doubt on the subject, that the matter to be referred to Richmond is the matter of the assassination of the President and others, to effect which these parties had previously agreed and conspired together. It is a matter in testimony, by the declaration of John H. Surratt, who is as clearly proved to have been in this conspiracy and murder as Booth himself, that about the very date of this letter, the 27th of March, upon the suggestion of Booth, and with his knowledge and consent, he went to Richmond, not only to see "how it would be taken there," but to get funds with which to carry out the enterprise, as Booth had already declared to Chester in one of his last interviews, when he said that he or "some one of the party" would be constrained to go to Richmond for funds to carry out the conspiracy. Surratt returned from Richmond, bringing with him some part of the money for which he went, and was then going to Canada, and, as the testimony discloses, bringing with him the despatches from Jefferson Davis to his chief agents in Canada, which, as Thompson declared to Conover, made the proposed assassination "all right." Surratt, after seeing the parties here, left immediately for Canada and delivered his despatches to Jacob Thompson, the agent of Jefferson Davis. This was done by Surratt upon the suggestion, or in exact accordance with the suggestion, of Arnold, made on the 27th of March in his letter to Booth just read, and yet you are gravely told that four weeks before the 27th of March Arnold had abandoned the conspiracy.

Surratt reached Canada with these despatches, as we have seen, about the 6th or 7th of April last, when the witness Conover saw them delivered to Jacob Thompson and heard their contents stated by Thompson, and the declaration from him that these despatches made it "all right." That Surratt was at that time in Canada is not only established by the testimony of Conover, but it is also in evidence that he told Wiechmann on the 3d of April that he was going to Canada, and on that day left for Canada, and afterwards, two letters addressed by Surratt over the fictitious signature of John Harrison, to his mother and to Miss Ward; dated at Montreal, were received by them on the 14th of April, as testified by Wiechmann and by Miss Ward, a witness called for the defense. Thus it appears that the condition named by Arnold in his letter had been complied with. Booth had "gone to Richmond," in the person of Surratt, "to see how it would be taken." The rebel authorities at Richmond had approved it, the agent had returned; and Arnold was, in his own words, thereby the better prepared to rejoin Booth in the prosecution of this conspiracy.

To this end Arnold went to Fortress Monroe. As his letter expressly declares, Booth said when they parted, "we would not meet in a month or so, and therefore I made application for employment—an answer to which I shall receive during the week." He did receive the answer that week from Fortress Monroe, and went there to await the "more propitious time," bearing with him the weapon of death which Booth had provided, and ready to obey his call, as the act had been approved at Richmond and been made "all right." Acting upon the same fact that the conspiracy had been approved in Richmond and the funds provided, O'Laughlin came to Washington to identify General Grant, the person who was to become the victim of his violence in the final consummation of this crime—General Grant, whom, as is averred in the specification, it had become the part of O'Laughlin by his agreement in this conspiracy to kill and murder. On the evening preceding the assassination—the 13th of April—by the testimony of three reputable witnesses, against whose truthfulness not one word is uttered here or elsewhere, O'Laughlin went into the house of the Secretary of War, where General Grant then was, and placed himself in position in the hall where he could see him, having declared before he reached that point, to one of these witnesses, that he wished to see General Grant. The house was brilliantly illuminated at the time; two, at least, of the witnesses conversed with the accused and the other stood very near to him, took special notice of his conduct, called attention to it, and suggested that he be put out of the house, and he was accordingly put out by one of the witnesses. These witnesses are confident, and have no doubt, and so swear upon their oaths, that Michael O'Laughlin is the man who was present on that occasion. There is no denial on the part of the accused that he was in Washington during the day and during the night of April 13, and also during the day and during the night of the 14th; and yet, to get rid of this testimony, recourse is had to that common device—an alibi; a device never, I may say, more frequently resorted to than in this trial. But what an alibi! Nobody is called to prove it, save some men who, by their own testimony, were engaged in a drunken debauch through the evening. A reasonable man who reads their evidence can hardly be expected to allow it to outweigh the united testimony of three unimpeached and unimpeachable witnesses who were clear in their statements, who entertain no doubt of the truth of what they say, whose opportunities to know were full and complete, and who were constrained to take special notice of the prisoner by means of his extraordinary conduct.

These witnesses describe accurately the appearance, stature, and complexion of the accused, but because they describe his clothing as dark or black, it is urged that as part of his clothing, although dark, was not black, the witnesses are mistaken. O'Laughlin and his drunken companions (one of whom swears that he drank ten times that evening) were strolling in the streets and in the direction of the house of the Secretary of War, up the Avenue; but you are asked to believe that these witnesses could not be mistaken in saying they were not off the Avenue above Seventh Street, or on K Street. I venture to say that no man who reads their testimony can determine satisfactorily all the places that were visited by O'Laughlin and his drunken associates that evening from seven to eleven o'clock P.M. All this time, from seven to eleven o'clock P.M., must be accounted for satisfactorily before the alibi can be established. O'Laughlin does not account for all the time, for he left O'Laughlin after seven o'clock, and rejoined him, as he says, "I suppose about eight o'clock." Grillet did not meet him until half-past ten, and then only casually saw him in passing the hotel. May not Grillet have been mistaken as to the fact, although he did meet O'Laughlin after eleven o'clock the same evening, as he swears?

Purdy swears to seeing him in the bar with Grillet about half-past ten, but, as we have seen by Grillet's testimony, it must have been after eleven o'clock. Murphy contradicts as to time both Grillet and Purdy, for he says it was half-past eleven or twelve o'clock when he and O'Laughlin returned to Rullman's from Platz's, and Early swears the accused went from Rullman's to Second Street to a dance about a quarter-past eleven o'clock, when O'Laughlin took the lead in the dance and stayed about one hour. I follow these witnesses no further. They contradict each other, and do not account for O'Laughlin all the time from seven to eleven o'clock. I repeat that no man can read their testimony without finding contradictions most material as to time, and coming to the conviction that they utterly fail to account for O'Laughlin's whereabouts on that evening. To establish an alibi the witnesses must know the fact and testify to it. Laughlan, Grillet, Purdy, Murphy, and Early utterly fail to prove it, and only succeed in showing that they did not know where O'Laughlin was all this time, and that some of them were grossly mistaken in what they testified, both as to time and place. The testimony of James B. Henderson is equally unsatisfactory. He is contradicted by other testimony of the accused as to place. He says O'Laughlin went up the Avenue above Seventh Street, but that he did not go to Ninth Street. The other witnesses swear he went to Ninth Street. He swears he went to Canterbury about nine o'clock, after going back from Seventh Street to Rullman's. Laughlan swears that O'Laughlin was with him at the corner of the Avenue and Ninth Street at nine o'clock, and went from there to Canterbury, while Early swears that O'Laughlin went up as far as Eleventh Street and returned with him and took supper at Welcker's about eight o'clock. If these witnesses prove an alibi, it is really against each other. It is folly to pretend that they prove facts which make it impossible that O'Laughlin could have been at the house of Secretary Stanton, as three witnesses swear he was, on the evening of the 13th of April, looking for General Grant.

Has it not, by the testimony thus reviewed, been established prima facie that in the months of February, March, and April, O'Laughlin had combined, confederated, and agreed with John Wilkes Booth and Samuel Arnold to kill and murder Abraham Lincoln, William H. Seward, Andrew Johnson, and Ulysses S. Grant? It is not established, beyond a shadow of doubt, that Booth had so conspired with the rebel agents in Canada as early as October last; that he was in search of agents to do the work on pay, in the interests of the rebellion, and that in this speculation Arnold and O'Laughlin had joined as early as February; that then, and after, with Booth and Surratt, they were in the "oil business," which was the business of assassination by contract as a speculation? If this conspiracy on the part of O'Laughlin with Arnold is established even prima facie, the declarations and acts of Arnold and Booth, the other conspirators, in furtherance of the common design, is evidence against O'Laughlin as well as against Arnold himself or the other parties. The rule of law is, that the act or declaration of one conspirator, done in pursuance or furtherance of the common design, is the act or declaration of all the conspirators.—1 Wharton, 706.

The letter, therefore, of his co-conspirator, Arnold, is evidence against O'Laughlin, because it is an act in the prosecution of the common conspiracy, suggesting what should be done in order to make it effective, and which suggestion, as has been stated, was followed out. The defense has attempted to avoid the force of this letter by reciting the statement of Arnold, made to Homer at the time he was arrested, in which he declared, among other things, that the purpose was to abduct President Lincoln and take him South; that it was to be done at the theatre by throwing the President out of the box upon the floor of the stage, when the accused was to catch him. The very announcement of this testimony excited derision that such a tragedy meant only to take the President and carry him gently away! This pigmy to catch the giant as the assassins hurled him to the floor from an elevation of twelve feet! The court has viewed the theatre, and must be satisfied that Booth, in leaping from the President's box, broke his limb. The court cannot fail to conclude that this statement of Arnold was but another silly device, like that of the "oil business," which, for the time being, he employed to hide from the knowledge of his captor the fact that the purpose was to murder the President. No man can, for a moment, believe that any one of these conspirators hoped or desired, by such a proceeding as that stated by this prisoner, to take the President alive in the presence of thousands assembled in the theatre after he had been thus thrown upon the floor of the stage, much less to carry him through the city, through the lines of your army, and deliver him into the hands of the rebels. No such purpose was expressed or hinted by the conspirators in Canada, who commissioned Booth to let these assassinations on contract. I shall waste not a moment more in combatting such an absurdity.

Arnold does confess that he was a conspirator with Booth in this purposed, murder; that Booth had a letter of introduction to Dr. Mudd; that Booth, O'Laughlin, Atzerodt, Surratt, a man with an alias "Mosby," and another whom he does not know, and himself, were parties to this conspiracy, and that Booth had furnished them all with arms. He concludes this remarkable statement to Horner with the declaration that at that time, to wit, the first week of March, or four weeks before he went to Fortress Monroe, he left the conspiracy, and that Booth told him to sell his arms if he chose. This is sufficiently answered by the fact that, four weeks afterwards, he wrote his letter to Booth, which was found in Booth's possession after the assassination, suggesting to him what to do in order to make the conspiracy a success, and by the further fact that at the very moment he uttered these declarations part of his arms were found upon his person, and the rest not disposed of, but at his father's house.