know it.

One of the chief assets of the big agency is its accumulated
information concerning all sorts of professional criminals.
Its galleries are quite as complete as those of the local
police headquarters, for a constant exchange of art objects is
going on with the police throughout the world. And as the
agency is protecting banks all over the United States it has
greater interest in all bank burglars as a class than the
police of any particular city who are only concerned with the
burglars who (as one might say) burgle in their particular
burg. Thus, you are more likely to find a detective from a
national agency than a sleuth from 300 Mulberry Street, New
York, following a forger to Australasia or Polynesia.

The best agencies absolutely decline to touch divorce and
matrimonial cases of any sort. It does not do a detective
agency any good to have its men constantly upon the witness
stand subject to attack, with a consequent possible reflection
upon their probity of character or truthfulness. Moreover, a
good detective is too valuable a person to be wasting his time
in the court-room. In the ordinary divorce case the
detective, having procured evidence, is obliged to remain on
tap and subject to call as a witness for at least three or
four months, during which time he cannot be sent away on
distant work. Neither can the customer be charged ordinarily
for waiting time, and apart from its malodorous character the
business is not desirable from a financial point of view.

The national agencies prefer clean criminal work, murder