If there is more than one murder, the subsequent victims should be more innocent than the initial victim, i.e., the murderer should start with a real grievance and, as a consequence of righting it by illegitimate means, be forced to murder against his will where he has no grievances but his own guilt.
Murder is negative creation, and every murderer is therefore the rebel who claims the right to be omnipotent. His pathos is his refusal to suffer. The problem for the writer is to conceal his demonic pride from the other characters and from the reader, since, if a person has this pride, it tends to appear in everything he says and does. To surprise the reader when the identity of the murderer is revealed, yet at the same time to convince him that everything he has previously been told about the murderer is consistent with his being a murderer, is the test of a good detective story.
As to the murderer's end, of the three alternatives—execution, suicide, and madness—the first is preferable; for if he commits suicide he refuses to repent, and if he goes mad he cannot repent, but if he does not repent society cannot forgive. Execution on the other hand, is the act of atonement by which the murderer is forgiven by society. In real life I disapprove of capital punishment, but in a detective story the murderer must have no future.
The detective-story society is a society consisting of apparently innocent individuals, i.e., their aesthetic interest as individuals does not conflict with their ethical obligations to the universal. The murder is the act of disruption by which innocence is lost, and the individual and the law become opposed to each other. In the case of the murderer this opposition is completely real (till he is arrested and consents to be punished); in the case of the suspects it is mosdy apparent.
But in order for the appearance to exist, there must be some element of reality; e.g., it is unsatisfactory if the suspicion is caused by chance or the murderer's malice alone. The suspects must be guilty of something, because, now that the aesthetic and the ethical are in opposition, if they are completely innocent (obedient to the ethical) they lose their aesthetic interest and the reader will ignore them.
For suspects, the principal causes of guilt are:
i) the wish or even the intention to murder;
2.) crimes of Class A or vices of Class C (e.g., illicit amours) which the suspect is afraid or ashamed to reveal;
a
a
a lack of faith in another loved suspect, which leads its subject to hide or confuse clues.
Completely satisfactory detectives are extremely rare. Indeed, I only know of three: Sherlock Holmes (Conan
Doyle), Inspector French (Freeman Wills Crofts), and Father Brown (Chesterton).