Dexter, a serial killer who preys on serial killers, used to be an emotionless flat-affect void like the type identified in Mark Seltzer's Wound Culture, motivated by bloodlust channeled into more or less acceptable channels by his police detective stepfather,
The "code" that Dexter's stepfather programmed into him when he discovered the boy exhibiting the early traits of a serial killer, specifically killing animals (he may have wet his bed and set fires as well to fit the classic pattern but the show does not tell us), assured that Dexter would only kill those who were a) likely to kill again and b) had somehow escaped the justice of legitimate law enforcement.
