The Ice Truck Killer took a curious array of victims as he taunted the title murderer in Dexter season 1, which included Dexter Morgan’s biological father. Dexter season 1 introduced the enigmatic vigilante serial killer Dexter Morgan, who struggled with his own humanity as he maintained a facade of "normalcy" during the day while moonlighting as a killer of murders that evaded the justice system. Dexter’s path to becoming a vigilante killer was abnormal, however, in that he was guided by a code given by his late adoptive policeman father Harry Morgan, who understood Dexter’s Dark Passenger after taking him in as a toddler.
Dexter season 1 sees the protagonist being taunted by the Ice Truck Killer, who uses personal details from Dexter’s past to reveal he knows his murderous secret. The killer turns out to be Brian Moser, Dexter’s biological brother who was also found in a shipping crate after their mother had been brutally murdered. Like Dexter, this traumatizing event created a Dark Passenger in Brian of the uncontrollable urge to kill, with the Ice Truck Killer spending season 1 trying to get Dexter to remember his origin of being “born in blood.”
Before the Ice Truck Killer is revealed to be Brian Moser, the murderer takes Dexter’s biological father as one of his victims, who Dexter didn’t even know existed. His adoptive father Harry had died long before these events, but Brian also held a grudge against him for only taking in Dexter after the tragedy. Brian’s core motivation in Dexter season 1 was to reconnect with his brother through their shared trauma and urge to kill, with the Ice Truck Killer’s murders being conducted as a way to either make Dexter remember his repressed past or remove anyone who stood in the way of their biological bond. Dexter’s biological father Joe Driscoll was the first victim to truly goad Dexter into digging into his origins, as the next logical step would be for Dexter to remember their biological mother, Laura Moser, whose death turned the boys into the killers they became.
Dexter never establishes whether Joe Driscoll was also the biological father of Brian, but the murder makes more sense if he’s not. If Joe was only Dexter’s father, killing him would be a way to resurface Dexter’s memory of their mother’s death while also removing him as a barrier between Dexter and Brian’s biological attachment. This also aligns with the reason why the Ice Truck Killer attempts to kill Dexter’s adoptive sister, Deb. The closest person in the world to Dexter was Debra, who he shared a much closer bond with than Brian, which clearly made him jealous. Brain’s lack of empathy for Debra or code for killing led him to think that Dexter was truly the same way, but Dexter’s protagonist had a genuine love for his non-biological sister – something Brian could never understand.
Since the Ice Truck Killer’s victims were largely prostitutes, the murder of Joe Driscoll was a specific target with the sole purpose of inciting Dexter to remember his past. Brian felt that killing Joe and Debra would have brought them closer together, especially after Dexter finally remembered their mother’s murder. However, the Code of Harry was so deeply embedded in his conscience that Dexter understood the Ice Truck Killer had to be put down, even if they were biological brothers. Had the Ice Truck Killer lived past Dexter season 1, he likely would have even murdered the innocent Rita as someone standing between their perceived bond.
The Ice Truck Killer takes Dexter's biological father as one of his victims in season 1, which had a specific purpose in taunting the protagonist.Jordan Williams