Esquirol attempted to define the nature of this invisible sickness that would exonerate the perpetrator of a monstrous crime, grouping together the symptoms: the subject always acted without an accomplice, and with no motive, his crime did not necessarily concern a person that he already knew, and once it had been carried out, 'everything was over for him, the goal was attained; after the murder he is calm, and no longer thinks of hiding'.