These examinations, it may be said, are compulsory at every step in promotion in the detective service, in addition to educational examinations carried out independently by the Civil Service Commissioners. Here is a question put at an examination for promotion to detective-sergeant which might form the skeleton of a detective story.
"A night-watchman, in going his rounds, discovers two men attempting to break open a safe on the premises. Both men make good their escape by a window, but one of them receives a blow on the head from the watchman which causes blood to flow, while the other leaves his jacket behind.
"The watchman can give a fair description of the men. In the jacket left behind, which bears no maker's name, are found the following:—(1) A return-half ticket to Birmingham from London; (2) A snapshot of a lady having the appearance of a music hall performer, signed 'Kitty,' but with no photographer's name; (3) a letter (no envelope) as follows:—
"King Street.
'Dear Tom.—I hope you are coming up on Tuesday. Things are bad here since Bill got his three months.
'Mary.'
"State as fully as you can what steps you suggest should be taken to trace the offenders. How could the articles found be made use of in the enquiry?"
The preliminary examination is only the first step. The young man who passes finds himself a "patrol on probation," with the knowledge that if he does not justify himself he will be returned to the blue-coated ranks. He is put to school again—the little-known detective school that is maintained at Scotland Yard, with Detective-Inspector Belcher at its head. There are lectures on law, and even lantern lectures. He is taught the methods of criminals, from gambling sharps to forgers, from pickpockets to petty sneak-thieves. The Black Museum primarily exists for his instruction. He is shown jemmies, coining implements, shop-lifting devices, and the latest word in the march of scientific burglary—the oxy-acetylene apparatus. All that ingenuity and experience can suggest for the confusion of the criminal is taught him. He is shown where an expert must be called in, and where his own common-sense must aid him. He is taught something of locks, something of finger-prints, something of cipher-reading. He learns the significance of trivialities, and the high importance of method.
I have said that the detective must know when to call in the expert. Science plays no inconspicuous part in many investigations, and there is a little corps of consulting specialists whose aid is always available. It was the work of the analyst that proved the guilt of men like Seddon and Crippen. The microscopist has brought more than one forger to justice. A murder was proved because a tool-maker's aid was enlisted to decipher some scratches on a chisel. A blackmailer was captured because a paper manufacturer identified a peculiar make of paper on which a letter was written. And, of course, the help of the medical jurisprudent is a commonplace of criminal investigation.
The finger-print experts are on the staff; so, too, are the photographers. There is a big magic lantern used in connection with the latter department which has made clear more than one mystery by the enlargement of some photograph. In one case an envelope with a blurred post-mark was picked up on the scene of a robbery. It was enlarged, and so the name of a town was picked out. In an hour or two the criminal was under arrest.