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). The job of the detective is to restore the state of grace in which the aesthetic and the ethical are as one. Since the murderer who caused their disjunction is the aesthetically defiant individual, his opponent, the detective, must be either the official representative of the ethical or the exceptional individual who is himself in a state of grace. If he is the former, he is a professional; if he is the latter, he is an amateur. In either case, the detective must be the total stranger who cannot possibly be involved in the crime; this excludes the local police and should, I think, exclude the detective who is a friend of one of the suspects. The professional detective has the advantage that, since he is not an individual but a representative of the ethical, he does not need a motive for investigating the crime; but for the same reason he has the disadvantage of being unable to overlook the minor ethical violations of the suspects, and therefore it is harder for him to gain their confidence.