"You recall handling this yesterday, I'm sure, Clayton.

I tried the same experiment with the lampblack on it this morning, you see.

And this"-- beside the notebook he placed the police photograph; that, too, in its enlargement, showed, sharply defined, a thumb print on a diamond-shaped background.

"You will no doubt recognise it as an official photograph, enlarged, taken of the gray seal on Metzer's forehead--AND THE THUMB PRINT OF METZER'S MURDERER.

You have only to glance at the little scar at the edge of the centre loop to satisfy yourself that the three are identical.