Chapter III: Elementary Principles

There is perhaps a greater demand for experienced detectives today than ever has been in the history of this country. That class of persons who seek to obtain a livelihood in violating the law, is constantly growing larger, and it is upon the detective, and the police department of the country that society must depend for protection from this menacing element.

In taking up detective work as a business in life, I would advise persons interested in this profession to first acquire some of the elementary principles. The young man or woman who hopes to make a success as a detective must learn something of the effect and cause. Every effect has its cause and while the cause of many effects is apparent, the detective often finds a situation the real cause of which is not self-evident. When I start out to conduct an investigation, the first thing I try is to determine the cause. That is, I try to ascertain a theory for the action. There must have been some motive for the offense, assuming, of course, it was committed by a normal, sane person.

Every crime presents some moral features that are intrinsic and essential. Such a feature is motive. “Who benefits by this crime?” is the first thing to be asked. This first step will eliminate many persons. The second clue should be found by answering the question. “Who had sufficient knowledge to commit the crime?” For instance, in a burglary where jewels or money are taken, the existence of which was known only to certain people. Thus many crimes are classified as inside jobs or outside jobs, meaning that some one inside the house committed the crime or that the evidence showed that someone entered the house from without.

Another point to be looked into is the character of the crime itself. Some crimes require real skill, such as forgery, bank robbery or counterfeiting. In this instance a knowledge of criminals and their peculiarities of work is essential to the detective and this knowledge is supplied only by experience.

The radius of action is another feature that calls for attention. This means that only people within a certain distance could have committed the crime, and all those outside that boundary can be eliminated. The proof of an alibi is the most simple counter to the detective.

A final caution must be given. Good judgment must be used in weighing the relative value of clues and the detective must not be too easily misled by appearances. Every claim must be tested and every physical fact must be verified. Where arrests are made the stories told by different suspects must be minutely examined and checked up, not only with other stories told, but also with physical facts of the case. For example, whether a door is locked on the inside or on the outside; whether glass that is broken falls to the inside or to the outside, whether blows can be struck from certain angles. The position of bullet marks on the walls, and a thousand other details must be carefully weighed, compared and classified before accurate deductions can be drawn.

Reconstruction is the greatest method of detection. While this involves, to a great extent, the creative imagination, it is, nevertheless, based upon a most minute collection of facts and cold experience in assigning them their proper places. While some great geniuses may be able to attain results by intuitive processes, it is a fact that practically all cases are solved by close observation, by common sense, by persistency and by understanding the meaning of evidence.

A final rule of universal application should be noted, and that is, the detective should always choose the most probable and least extravagant hypothesis to work upon. He should base his reasoning upon the common facts of human nature and the common occurrences of physical events, rather than be led away into fantastic suppositions by many points that at the same time seem mysterious and incapable of a rational explanation.