communicated to me while at Detroit, there is no doubt that Mr. Jacob Thompson, Secretary of the Interior under Mr. Buchanan, was in the vicinity of Sandwich, staying with Colonel Steele, a Southerner and a violent secessionist, and that the piratical expedition was set on foot under his auspices and by the aid of means contributed by him. He was at Colonel Steele's house as late as Saturday, the 17th of September. His complicity with the transaction can be ascertained and proved, if the measure recommended in my confidential letter of the 24th instant is adopted. It can be made to appear that Mr. Thompson, an authorized agent of the insurgent authorities at Richmond, is residing in Canada, under British protection, and was engaged in at least one instance in setting on foot military enterprises against the United States, and in another in organizing a piratical expedition against the property of its citizens. I called the attention of Mr. Macdonell to this fact, explaining to him the relation in which Mr. Tompson stands to the leaders of the rebellion, and independently of the facts disclosed, making it manifest that he could not be in Canada, and especially on the Detroit River, where the water boundary between the United States and Canada is less than a mile wide, for any other than purpose of mischief.

The object of the expedition can only be gathered from the declarations of the leaders. They were declared to be the release of the prisoners on Johnson's Island and the capture of the Michigan. The party did not exceed thirty in number, while there was a large force on Johnson's Island and from 100 to 200 men on board the Michigan. It is, therefore, quite clear that neither of the objects said to have been in view could have been accomplished without the co-operation of an armed force in Sandusky. Whether any such co-operation was arranged can only be ascertained through the confessions of Cole, referred to in Appendix A 1 to A 5, or through a searching judicial investigation. Cole, who was leading an infamous life at Sandusky, with means unquestionably furnished by the rebel authorities, is now in custody at Fort Johnson, and the only question in regard to him is whether he should be tried and executed as a spy, or whether he should be pardoned on making a full disclosure of the plot with he was connected, and the identification of his accomplices.

On arriving at Sandusky, I found Major-General Hitchcock in communication with the commanding officer at Johnson's Island and the commander of the Michigan, and I deemed it unnecessary to enter into an investigation which had been carried by them as far as it could be without the intervention of a court, with power to compel the attendance of witnesses. The result of the investigation discloses, in brief, the following principal facts:

1. An armed force was organized at Windsor, Canada, and its vicinity, for hostile purposes, to be executed in the United States.

2. The party captured and took forcible possession of two steamers in the waters of the United States.

3. One of the captured steamers was scuttled in the waters of the United States, and the other in British waters and at a British dock.

4. The engineer of one of the steamers was shot, though not fatally, and several others were wounded.

5. Two of the parties to these outrages were arrested and taken before two British magistrates at Sandwich, the place where on e of the steamers was plundered and scuttled, and were discharged without a formal examination.