Benjamin J. Cross, a prisoner confined in the Old Capitol Building, I have the honor to report as follows:

I find on file in my office a letter addressed to yourself of which the following is a copy and which seems to be the initiation of the case:

HEADQUARTERS CORPS OF OBSERVATION, Poolesville, Md., October 10, 1861.

Brigadier General A. PORTER,
Provost-Marshal, Army of the Potomac, Washington, D. C.

GENERAL: I forward to you as a prisoner Mr. [B.] Jackson Cross who was this morning arrested by the Thirty-fourth Regiment New York Volunteers at Seneca. Mr. Cross is brother-in-law of Doctor Causten, a member of the President's Mounted Guard lately in the service of the United States from the District of Columbia, who was taken prisoner in his own house near Seneca in May last by Virginia troops said to have been led there by this Mr. Cross. Lieutenant Colonel Samuel [W.] Owen, of the Kentucky [Pennsylvania] Cavalry (Colonel Averell), was captain of the company and can give testimony or information in the case. Mr. Causten, notary public on F street near Fifteenth, can also give information. Young Mr. Causten yet remains a prisoner in the hands of the rebels by the act as it is alleged of this Mr. Cross.

Very respectfully, I am, general, your most obedient servant,

CHAS. P. STONE,

Brigadier-General, Commanding.

[Indorsement on back of the letter.]

WASHINGTON, D. C., October 11, 1861.

I believe the facts herein stated to be true.

S. W. OWEN,

Lieutenant-Colonel Kentucky [Pennsylvania] Cavalry.

On the 7th of November I detailed one of my operatives to further investigate the matter. He learned from two nieces of young Causten at the residence of their grandfather on F street, near Fifteenth, that their uncle, the Doctor Causten above mentioned, was a brother-in-law of Cross; that they had understood that on the day before their uncle's arrest he went to the house of Cross at his (Cross') invitation, where he was captured by Virginia troops said t ohave been guided there by Cross. They further stated that they had been informed that their uncle was then a prisoner at Raleigh, N. C. ; that Lieutenant-Colonel Owen knew more of the matter, &c.

On the 8th of November the same operative visited the camp of the Kentucky [Pennsylvania] cavalry on the Virginia side of the Potomac for the purpose of examining Lieutenant-Colonel Owen on the subject. Colonel Owen stated that Causten, the man who it was alleged had been betrayed to the rebels by Cross, was a member of the President's Mounted Guard of which he (Owen) was captain and which was in the service of the United States; that some time in May last Causten went to the house of Cross in Seneca, Md., to see has wife who was on a visit there, she being a sister of Mrs. Cross; that while he was there an officer of the Virginia army by the name of White came with a detachment of rebel soldiers and took him prisoner, carrying him to Virginia where he has been ever since; that he (Owen) went with the District volunteers to the vicinity of Seneca, near Edwards Ferry, a short time after the capture of Causten and remained there four or five weeks; that while there he had the house of Cross watched all the time and Cross never came to it; that on inquiry he learned that on the day of Causten's capture Cross was seen to go over the river at Edwards Ferry into Virginia; that a short afterward White with his squad of men crossed over from Virginia at the ferry, proceeded straight to Cross' house, captured Causten and returned with him into Virginia; that it was the belief of all the persons in the vicinity who were cognizant