[https://dexter.fandom.com/wiki/Doris_Morgan Doris Morgan], Dexter's adoptive mother, dies of [[cancer]] when he is 16. When Dexter reaches puberty, he realizes that he is uninterested in sex and needs instruction by his father on how to behave with women. Around this time, Harry discovers that Dexter has been killing neighborhood pets and realizes that the boy has an innate need to kill. Harry decides to channel Dexter's urges in a "positive" direction by teaching him to kill people who "deserve it", and to get rid of any evidence so he does not get caught.
When Dexter is 18, Harry is diagnosed with cancer and hospitalized. There, Harry gives Dexter his "permission" to kill his first human victim, a nurse who is murdering her patients with overdoses of morphine.