They found that a genotype conferring low levels of the enzyme monoamine oxidase A (MAOA), when combined with early child abuse, predisposed the individual to later antisocial behavior.

WSJ: Neurocriminology: Inside the Criminal Mind

After analyzing data from 47 independent brain imaging studies, researchers found that the rule-breaking behavior common to people with antisocial, violent, and psychopathic tendencies may result partly from damage to the neural circuitry in the brain that underlies moral decision-making.

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