“The riddle, so far, was now unriddled.  The assassin had escaped through the window which looked upon the bed.  Dropping of its own accord upon his exit (or perhaps purposely closed), it had become fastened by the spring; and it was the retention of this spring which had been mistaken by the police for that of the nail, — farther inquiry being thus considered unnecessary.

“The next question is that of the mode of descent.  Upon this point I had been satisfied in my walk with you around the building.  About five feet and a half from the casement in question there runs a lightning-rod.  From this rod it would have been impossible for any one to reach the window itself, to say nothing of entering it.  I observed, however, that the shutters of the fourth story were of the peculiar kind called by Parisian carpenters ferrades — a kind rarely employed at the present day, but frequently seen upon very old mansions at Lyons and Bourdeaux.  They are in the form of an ordinary door, (a single, not a folding door) except that the lower half is latticed or worked in open trellis — thus affording an excellent hold for the hands.  In the present instance these shutters are fully three feet and a half broad.  When we saw them from the rear of the house, they were both about half open — that is to say, they stood off at right angles from the wall.  It is probable that the police, as well as myself, examined the back of the tenement; but, if so, in looking at these ferrades in the line of their breadth (as they must have done), they did not perceive this great breadth itself, or, at all events, failed to take it into due consideration.  In fact, having once satisfied themselves that no egress could have been made in this quarter, they would naturally bestow here a very cursory examination.  It was clear to me, however, that the shutter belonging to the window at the head of the bed, would, if swung fully back to the wall, reach to within two feet of the lightning-rod.  It was also evident that, by exertion of a very unusual degree of activity and courage, an entrance into the window, from the rod, might have been thus effected. — By reaching to the distance of two feet and a half (we now suppose the shutter open to its whole extent) a robber might have taken a firm grasp upon the trellis-work.  Letting go, then, his hold upon the rod, placing his feet securely against the wall, and springing boldly from it, he might have swung the shutter so as to close it, and, if we imagine the window open at the time, might even have swung himself into the room.

“I wish you to bear especially in mind that I have spoken of a very unusual degree of activity as requisite to success in so hazardous and so difficult a feat.  It is my design to show you, first, that the thing might possibly have been accomplished:  — but, secondly and chiefly, I wish to impress upon your understanding the very extraordinary — the almost præternatural character of that agility which could have accomplished it.