<P> A string of murders of prostitutes leads to the identification of a new serial killer called "The Ice Truck Killer", due to how the victims' bodies are well - preserved by being kept chilled before they are found . Dexter identifies patterns of the serial killer from his own habits, and lets Debra know, helping the department get a lead on the killer and leading to Debra's promotion to Homicide . Her investigation leads her to meet Rudy Cooper, a prosthetics expert, and they start a relationship . Meanwhile, Dexter discovers that the Ice Truck Killer has broken into his apartment and left taunting clues, leading Dexter to believe that the Killer is playing a game with him . </P> <P> During the investigation of the Killer, Dexter discovers that his biological father, Joe Driscoll, had only died recently, leading him to question his memories of how his mother died . A gruesome, blood - filled murder scene causes Dexter to recall exactly what had happened: criminals had placed him and his mother, Laura Moser, in a shipping container, killed Laura and dismembered her with chainsaws, and locked Dexter up in the container in a pool of his mother's blood, rescued by Harry two days later . Harry had purposely altered the records to prevent Dexter from finding out . </P> <P> Through Debra, Rudy tries to get closer to Dexter . Dexter comes first to realize that Rudy killed Joe, and later affirms that he is the Ice Truck Killer . With his identity blown, Rudy kidnaps Debra and draws Dexter into a trap to rescue her . Rudy reveals to Dexter that he is his older brother Brian Moser, also left in the shipping container when Laura was killed . However, unlike Dexter, he was sent off to live in series of mental institutions . Brian too has developed serial killer tendencies, but did not have the morals that Harry instilled in Dexter, and used the Ice Truck Killer approach to help Dexter recall his past . Brian suggests to Dexter they kill Debra together, but Dexter refuses . Brian gets away after a fight, and Dexter rescues Debra . </P> <P> As police investigate, Doakes suspects Dexter of being the Ice Truck Killer, but Debra vouches for him . Brian attempts to capture Debra again, but falls into a trap laid by Dexter . Dexter apologizes to Brian before killing him, though leaving Brian's body to make it appear as suicide . The police rule the Ice Truck Killer case closed, though Doakes keeps close tabs on Dexter, still suspicious of his actions . Rita discovers evidence that Dexter may have set up Paul . </P>

Who was the ice truck killer on dexter