thumb-print could have been introduced by any person?"

"No," answered the lawyer. "It is quite impossible. The paper on which
the mark was found was a leaf from Mr. Hornby's memorandum block. He had
pencilled on it some particulars relating to the diamonds, and laid it
on the parcel before he closed up the safe."

"Was anyone present when Mr. Hornby opened the safe in the morning?"
asked Thorndyke.

"No, he was alone," answered the lawyer. "He saw at a glance that the
diamonds were missing, and then he observed the paper with the
thumb-mark on it, on which he closed and locked the safe and sent for
the police."

"Is it not rather odd that the thief did not notice the thumb-mark,
since it was so distinct and conspicuous?"

"No, I think not," answered Mr. Lawley. "The paper was lying face
downwards on the bottom of the safe, and it was only when he picked it
up and turned it over that Mr. Hornby discovered the thumb-print.
Apparently the thief had taken hold of the parcel, with the paper on it,
and the paper had afterwards dropped off and fallen with the marked
surface downwards--probably when the parcel was transferred to the other
hand."

"You mentioned," said Thorndyke, "that the experts at Scotland Yard have
identified this thumb-mark as that of Mr. Reuben Hornby. May I ask how
they came to have the opportunity of making the comparison?"