[OFFICIAL.]

WAR DEPARTMENT, WASHINGTON, April 15 -- 1:30 A.M.

Maj.-Gen. Dix:

This evening at about 9:30 P.M., at Ford's Theatre, the President, while sitting in his private box with Mrs. LINCOLN, Mrs. HARRIS, and Major RATHBURN, was shot by as assassin, who suddenly entered the box and approached behind the President.

The assassin then leaped upon the stage, brandishing a large dagger or knife, and made his escape in the rear of the theatre.

The pistoi ball entered the back of the President's head and penetrated nearly through the head. The wound is mortal. The President has been insensible ever since it was inflicted, and is now dying.

About the same hour an assassin, whether the same or not, entered Mr. SEWARD's apartments, and under the pretence of having a prescription, was shown to the Secretary's sick chamber. The assassin immediately rushed to the bed, and inflicted two or three stabs on the throat and two on the face. It is hoped the wounds may not be mortal. My apprehension is that they will prove fatal.