corroboration--a most dangerous and misleading statement which has been
fastened upon eagerly by the police, who have naturally been delighted
at obtaining a sort of magic touchstone by which they are saved the
labour of investigation. But there is no such thing as a single fact
that 'affords evidence requiring no corroboration.' As well might one
expect to make a syllogism with a single premise." "I suppose they
would hardly go so far as that," I said, laughing.

"No," he admitted. "But the kind of syllogism that they do make is
this--

"'The crime was committed by the person who made this finger-print.

"'But John Smith is the person who made the finger-print.

"'Therefore the crime was committed by John Smith.'"

"Well, that is a perfectly good syllogism, isn't it?" I asked.

"Perfectly," he replied. "But, you see, it begs the whole question,
which is, 'Was the crime committed by the person who made this
finger-print?' That is where the corroboration is required."

"That practically leaves the case to be investigated without reference
to the finger-print, which thus becomes of no importance."

"Not at all," rejoined Thorndyke; "the finger-print is a most valuable
clue as long as its evidential value is not exaggerated. Take our
present case, for instance. Without the thumb-print, the robbery might
have been committed by anybody; there is no clue whatever. But the