<P> It is later discovered that, before these three, the Trinity Killer also kidnaps a young boy whom he dresses in cowboy pajamas and convinces to play with a train set in a recreation of his childhood . Following this, he will bury the boy alive in cement at a Four Walls' building site . These killings were not connected to the pattern until shortly before Mitchell's death, because the boys were reported as missing rather than dead . </P> <P> At first, Dexter Morgan is fascinated by Mitchell's efficient killing methods and apparent ability to balance his familial responsibilities with his secret life as a serial killer . </P> <P> Mitchell lives with his wife, Sally, and his teenaged children, Jonah and Rebecca . He has another, older daughter by a previous relationship: Christine Hill, who witnessed one of his murders as a child . He treats her like a shameful secret, forbidding her from contacting him and keeping her existence hidden from his other family . She tries unsuccessfully to win his love, going so far as to commit murder for him; she kills FBI agent Frank Lundy and wounds Dexter's adopted sister Debra to protect her father from the police . Her actions have the opposite of the intended effect, however: When he learns what she has done, Mitchell tells her he wishes she had never been born . She commits suicide shortly afterward . </P> <P> Members of his family died in the same way as his victims: his sister died in a bathtub in 1959, his mother jumped to her death in 1961, and his father was bludgeoned to death (presumably by Arthur himself) in 1962 . </P>

Who shot dexter's sister in season 4