After some further conversation, the President asked General Butler for his professional opinion, as to whether Davis, Benjamin, Floyd, Wigfall, and the other civil officers of the Confederacy, could be tried by a military commission. General Butler replied that if they could be arrested in the insurrectionary States--in any locality under military control and where no civil authority existed or was recognized--they could be arraigned before such a tribunal, but a court of this character would have no jurisdiction if the criminals should get upon foreign soil, or, before being apprehended, reach any district where the civil law was in force. Mr. Chandler then urged that Davis should, by all means, be secured before he had a chance to leave the seceded States; and inquired as to the situation of the troops in the South and the probability of their defeating an attempt by Davis to fly through Mexico, or by boat on the Gulf. President Johnson replied that no way was open for his escape, but that he would be captured, dead or alive. The supposition that Davis was implicated in the assassination plot was then discussed with some difference of opinion, and finally the President asked General Butler to indicate a plan for the prosecution and punishment of Davis and his associates, for the use of the government. General Butler consented and the conference ended. With the preparation of the memorandum thus requested, General Butler occupied almost his entire time for several weeks, investigating precedents, and examining authorities with the utmost thoroughness. During this work he was repeatedly in consultation with Mr. Chandler, who saw all of his notes and made many suggestions; before its completion, Davis had been captured and sent to Fortress Monroe. General Butler's plan was submitted to President Johnson in the latter part of May, 1865. It was long and elaborate, was based upon an exhaustive examination of the history of all military tribunals, and set forth in substance these propositions: 1. That Davis could be tried by a military commission, having been captured while in rebellion in a locality where no lawful civil authority existed. This tribunal could sit at Fortress Monroe, where Davis was a prisoner, as that was still within the military lines. 2. That this commission should be composed of the thirteen officers of the highest rank in the army; this provision would have made it consist of Lieut.-Gen. U. S. Grant; Major-Generals H. W. Halleck, W. T. Sherman, George G. Meade, Philip H. Sheridan, George H. Thomas, and Brigadier-Generals Irwin McDowell, Wm. S. Rosecrans, Philip St. George Cooke, John Pope, Joseph Hooker, W. S. Hancock, and John M. Schofield.