When I had examined everything else, I turned my attention to the chair.

I did not expect it to tell me anything, yet it was from it that I obtained the clue that was ultimately to lead to the solution of the whole mystery.
The chair was a cheap one, made of white wood, and had the usual smooth strip of wood at the top.

On the back of this piece of wood, a quarter of an inch or so from the bottom, on the left-hand side, was a faint smear of blood.

The presence of the blood set me thinking.

When found, the chair had been exactly eighteen inches from the body.