Thus, before the outer door were stormed, the King would be dead.

And his body?
For his body would be evidence as damning as himself.
"Nay, sir," said Johann, "his Highness has thought of that.

While the two hold the outer room, the one who has killed the King unlocks the bars in the square window (they turn on a hinge).

The window now gives no light, for its mouth is choked by a great pipe of earthenware; and this pipe, which is large enough to let pass through it the body of a man, passes into the moat, coming to an end immediately above the surface of the water, so that there is no perceptible interval between water and pipe.

The King being dead, his murderer swiftly ties a weight to the body, and, dragging it to the window, raises it by a pulley (for, lest the weight should prove too great, Detchard has provided one) till it is level with the mouth of the pipe.