to commit the crime springs from a slow and reflective process which increases from the weak or static (obsession) state until it becomes an irresistible impulse and takes a violent and dynamic form, finding vent in the criminal act, is very frequent under the influence of the delusion of persecution, in chronic alcoholics, in hysterical subjects, etc., and is also seen in other non-violent forms of mental alienation. Sometimes the madman has a perfect cognizance of his own madness, so that he will often warn others as to the crime he intends to commit and knows the punishment due to it, and yet nevertheless this will not deter him unless fortuitous external causes intervene. In fact, it often happens that madmen affected by homicidal obsession, incapable of restraining themselves, afraid of themselves, in order not to yield to the homicidal impulse, take the precaution of wounding or mutilating themselves, in order thus to divert their ungovernable impulse, and render it impossible to execute their purpose. A case in point is that of a man who, unable to dominate the violent force impelling him to murder his wife and children, consigned himself to the police and had himself shut up in an asylum.
The second type, in which the determination to homicide proceeds from a spontaneous impulse (the transitory mania of the old school of psychiatry), from a species of impulsive vertigo, without a real impulse or motive, is found generally in epileptic subjects. This tyrannous impulse toward crime is also due very frequently to hallucination and illusion, often ignored by those who have to do with madmen. Homicide from hallucination presents three subtypes: first, that in which the madman acts under the terror of a fearful hallucination (epileptics, alcoholics, etc.); secondly, in consequence of delirium from delirious homicidal premises (persecution mania); thirdly, in obedience to the imperious commands of an inward voice. Nevertheless, this does not exclude the criminal motive (vendetta, jealousy, etc.) which sometimes determines the insane to commit homicide (especially the epileptics), motives which they readily, however, confess.
To complete the psycho-pathological characteristics as to the deliberate moment of homicide in the insane, Ferri treats of homicide as an end in itself or as a means toward a legitimate end, observing that if in mad homicides murder is an end in itself (killing to kill, impulse without motive) or as a means to an end, more often social and juridic (defense from imaginary perils, withdrawal of their victim from misery, etc.), in common madmen it is always a means to reach an antisocial end. This remark is all the more important because, besides refuting the ancient affirmation which is still repeated, that delinquents have always a motive for their deed, while madmen have none, it also refutes the other no less erroneous affirmation of Esquirol