"Red
Bob," etc., etc., one name or another being put forward according to the
kind of crime I was investigating.

It was easy to test my prosaic subordinate's statements by methods with
which I was familiar in secret-service work; and I soon found that he
was generally right. Great crimes are the work of great criminals, and
great criminals are very few. And by "great crimes" I mean, not crimes
that loom large in the public view because of their moral heinousness,
but crimes that are the work of skilled and resourceful criminals. The
problem in such cases is not to find the offender in a population of
many millions, but to pick him out from among a few definitely known
"specialists" in the particular sort of crime under investigation.

A volume might be filled with cases to illustrate my meaning; but a very
few must here suffice. It fell upon a day, for example, that a "ladder
larceny" was committed at a country house in Cheshire. It was the usual
story. While the family were at dinner, the house was entered by means
of a ladder placed against a bedroom window, all outer doors and
ground-floor windows having been fastened from outside by screws or wire
or rope; and wires were stretched across the lawn to baffle pursuit in
case the thieves were discovered. The next day the Chief Constable of
the county called on me; for, as he said, such a crime was beyond the
capacity of provincial practitioners, and he expected us to find the
delinquents among our pets at Scotland Yard. He gave me a vague
description of two strangers who had been seen near the house the day
before, and in return I gave him three photographs. Two of these were
promptly identified as the men who had come under observation. Arrest
and conviction followed, and the criminals received "a punishment suited
to their sin." One of them was "Quiet Joe"; the other, his special
"pal."

Their sentences expired about the time of my retirement from office, and
thus my official acquaintance with them came to an end. But in the
newspaper reports of a similar case the year after I left office, I
recognized my old friends. Rascals of this type are worth watching, and
the police had noticed that they were meeting at the Lambeth Free
Library, where their special study was provincial directories and books
of reference. They were tracked to a bookshop where they bought a map of
Bristol, and to other shops where they procured the plant for a "ladder
larceny." They then book