"The Ice Truck Killer", a serial killer eluding the Miami PD, has been communicating with Dexter through his crime scenes. Sgt. James Doakes (Erik King) suspects that Dexter has some connection to the Ice Truck Killer and starts to keep him under surveillance. After repeated attempts to get back in Rita’s life, Dexter sets up Paul to look like he violated his parole. While back in prison proclaiming his innocence, Paul points Rita to a clue to the truth about Dexter, which she dismisses.
Debra begins dating a man named Rudy, who is later revealed to be the Ice Truck Killer. Rudy also reveals to Dexter alone that he is his biological brother, Brian Moser. He describes additional details of Dexter's early childhood to him. The formative event for the brothers was witnessing their mother and several other people being butchered by a drug dealer and being locked in a cargo container for two days with the dismembered corpses, the floor covered in blood. Brian spent much of his childhood institutionalized. Harry, the officer who freed the boys, deliberately hid the details about the crime from Dexter, as well as information about his biological family.
Brian kidnaps Debra with the intention that he and Dexter would kill her together to cement their bond and sever the ties between Dexter and his adoptive family. Dexter instead turns against Brian and ultimately kills him, making the death look like a suicide. Everyone, including Debra, remains unaware of the exact connection between Dexter and Rudy/Brian. Dexter feels some regret over killing Brian, the one person who fully understood him, in order to save Debra, whom he knows would turn away from him if she ever learned his true nature.
