The most successful, and therefore perhaps the greatest, criminal in Shakespeare is King Claudius of Denmark. His murder of his brother by pouring a deadly poison into his ear while sleeping, is so skilfully perpetrated as to leave no suspicion of foul play. But for a supernatural intervention, a contingency against which no murderer could be expected to have provided, the crime of Claudius would never have been discovered. Smiling, jovial, genial as M. Derues or Dr. Palmer, King Claudius might have gone down to his grave in peace as the bluff hearty man of action, while his introspective nephew would in all probability have ended his days in the cloister, regarded with amiable contempt by his bustling fellowmen. How Claudius got over the great difficulty of all poisoners, that of procuring the necessary poison without detection, we are not told; by what means he distilled the "juice of cursed hebenon"; how the strange appearance of the late King's body, which "an instant tetter" had barked about with "vile and loathsome crust," was explained to the multitude we are left to imagine. There is no real evidence to show that Queen Gertrude was her lover's accomplice in her husband's murder. If that had been so, she would no doubt have been of considerable assistance to Claudius in the preparation of the crime. But in the absence of more definite proof we must assume Claudius' murder of his brother to have been a solitary achievement, skilfully carried out by one whose genial good-fellowship and convivial habits gave the lie to any suggestion of criminality. Whatever may have been his inward feelings of remorse or self-reproach, Claudius masked them successfully from the eyes of all. Hamlet's instinctive dislike of his uncle was not shared by the members of the Danish court. The "witchcraft of his wit," his "traitorous gifts," were powerful aids to Claudius, not only in the seduction of his sister-in-law, but the perpetration of secret murder.
The case of the murder of King Duncan of Scotland by Macbeth and his wife belongs to a different class of crime. It is a striking example of dual crime, four instances of which are given towards the end of this book. An Italian advocate, Scipio Sighele, has devoted a monograph to the subject of dual crime, in which he examines a number of cases in which two persons have jointly committed heinous crimes.3 He finds that in couples of this kind there is usually an incubus and a succubus, the one who suggests the crime, the other on whom the suggestion works until he or she becomes the accomplice or instrument of the stronger will; "the one playing the Mephistophelian part of tempter, preaching evil, urging to crime, the other allowing himself to be overcome by his evil genius." In some cases these two roles are clearly differentiated; it is easy, as in the case of Iago and Othello, Cassius and Brutus, to say who prompted the crime. In others the guilt seems equally divided and the original suggestion of crime to spring from a mutual tendency towards the adoption of such an expedient. In Macbeth and his wife we have a perfect instance of the latter class. No sooner have the witches prophesied that Macbeth shall be a king than the "horrid image" of the suggestion to murder Duncan presents itself to his mind, and, on returning to his wife, he answers her question as to when Duncan is to leave their house by the significant remark, "To-morrow—as he proposes." To Lady Macbeth from the moment she has received her husband's letter telling of the prophecy of the weird sisters, murder occurs as a means of accomplishing their prediction. In the minds of Macbeth and his wife the suggestion of murder is originally an auto-suggestion, coming to them independently of each other as soon as they learn from the witches that Macbeth is one day to be a king. To Banquo a somewhat similar intimation is given, but no foul thought of crime suggests itself for an instant to his loyal nature. What Macbeth and his wife lack at first as thorough-going murderers is that complete insensibility to taking human life that marks the really ruthless assassin. Lady Macbeth has the stronger will of the two for the commission of the deed. It is doubtful whether without her help Macbeth would ever have undertaken it. But even she, when her husband hesitates to strike, cannot bring herself to murder the aged Duncan with her own hands because of his resemblance as he sleeps to her father. It is only after a deal of boggling and at serious risk of untimely interruption that the two contrive to do the murder, and plaster with blood the "surfeited grooms." In thus putting suspicion on the servants of Duncan the assassins cunningly avert suspicion from themselves, and Macbeth's killing of the unfortunate men in seeming indignation at the discovery of their crime is a master-stroke of ingenuity. "Who," he asks in a splendid burst of feigned horror, "can be wise, amazed, temperate and furious, loyal and natural in a moment?" At the same time Lady Macbeth affects to swoon away in the presence of so awful a crime. For the time all suspicion of guilt, except in the mind of Banquo, is averted from the real murderers. But, like so many criminals, Macbeth finds it impossible to rest on his first success in crime. His sensibility grows dulled; he "forgets the taste of fear"; the murder of Banquo and his son is diabolically planned, and that is soon followed by the outrageous slaughter of the wife and children of Macduff. Ferri, the Italian writer on crime, describes the psychical condition favourable to the commission of murder as an absence of both moral repugnance to the crime itself and the fear of the consequences following it. In the murder of Duncan, it is the first of these two states of mind to which Macbeth and his wife have only partially attained. The moral repugnance stronger in the man has not been wholly lost by the woman. But as soon as the crime is successfully accomplished, this repugnance begins to wear off until the King and Queen are able calmly and deliberately to contemplate those further crimes necessary to their peace of mind. But now Macbeth, at first the more compunctious of the two, has become the more ruthless; the germ of crime, developed by suggestion, has spread through his whole being; he has begun to acquire that indifference to human suffering with which Richard III. and Iago were gifted from the first. In both Macbeth and Lady Macbeth the germ of crime was latent; they wanted only favourable circumstances to convert them into one of those criminal couples who are the more dangerous for the fact that the temptation to crime has come to each spontaneously and grown and been fostered by mutual understanding, an elective affinity for evil. Such couples are frequent in the history of crime. Eyraud and Bompard, Mr. and Mrs. Manning, Burke and Hare, the Peltzer brothers, Barre and Lebiez, are instances of those collaborations in crime which find their counterpart in history, literature, drama and business. Antoninus and Aurelius, Ferdinand and Isabella, the De Goncourt brothers, Besant and Rice, Gilbert and Sullivan, Swan and Edgar leap to the memory.
In the cases of Eyraud and Bompard, both man and woman are idle, vicious criminals by instinct. They come together, lead an abandoned life, sinking lower and lower in moral degradation. In the hour of need, crime presents itself as a simple expedient for which neither of them has any natural aversion. The repugnance to evil, if they ever felt it, has long since disappeared from their natures. The man is serious, the woman frivolous, but the criminal tendency in both cases is the same; each performs his or her part in the crime with characteristic aptitude. Mrs. Manning was a creature of much firmer character than her husband, a woman of strong passions, a redoubtable murderess. Without her dominating force Manning might never have committed murder. But he was a criminal before the crime, more than suspected as a railway official of complicity in a considerable train robbery; in his case the suggestion of murder involved only the taking of a step