Murder in ordinary cases, where the sympathy is wholly directed to the case of the murdered person, is an incident of coarse and vulgar horror; and for this reason, that it flings the interest exclusively upon the natural but ignoble instinct by which we cleave to life; an instinct, which, as being indispensable to the primal law of self-preservation, is the same in kind, (though different in degree,) amongst all living creatures; this instinct therefore, because it annihilates all distinctions, and degrades the greatest of men to the level of “the poor beetle that we tread on,” exhibits human nature in its most abject and humiliating attitude. Such an attitude would little suit the purposes of the poet. What then must he do? He must throw the interest on the murderer. Our sympathy must be with _him_; (of course I mean a sympathy of comprehension, a sympathy by which we enter into his feelings, and are made to understand them,–not a sympathy of pity or approbation.) In the murdered person all strife of thought, all flux and reflux of passion and of purpose, are crushed by one overwhelming panic; the fear of instant death smites him “with its petrific mace.” But in the murderer, such a murderer as a poet will condescend to, there must be raging some great storm of passion,–jealousy, ambition, vengeance, hatred,–which will create a hell within him; and into this hell we are to look.
Thomas de Quincey