Zach is a young Caucasian male with mid-length, combed-forward brown hair and green eyes. He is fairly pale, and clean-shaven with a fit, athletic frame. He dresses like a rich preppie, in buttoned-down shirts with khaki shorts and shoes.
His kill attire is similar to Dexter's. It is a tight, black long-sleeved shirt, dark pants, shoes, and black gloves.
Zach is an eerie yet inquisitive youth, who quickly inserts himself into the detectives' questioning of his father about the death of a woman Zach's father seemed to be sleeping with. Zach seemed concerned about what his father might say or what the police might know...suggesting he Zach killed the girl or had some involvement (which he did). Zach later approaches Dexter, who was on the scene, questioning Dexter about his knowledge and analysis of Norma Rivera's murder scene.
Zach is a psychopath whose murderous impulses have developed under unknown circumstances. He is excited by the sight of blood, takes pictures of crime scenes, and "touches up" the photos to breathe more life into his "art". When he kills someone, he describes the feeling as a heavy weight being lifted off his chest and, and he feels that he finally has something under his control. Unfortunately, he is mistaken, as his urges are truly chaotic. Unlike his tutor Dexter Morgan, who grew up from early childhood with Harry by his side, Zach didn't receive a mentor until his late teens, after his psychopathic instincts had already embedded themselves deep in his mind, making his urge to kill intensely strong and potentially stronger than his own willpower.
After speaking to a witness who recognized Zach driving in a Porsche nearby during the time that Norma Rivera was pummeled to death, Quinn pursues him, only to be told to back off by Deputy Chief Matthews after the witness apparently recants his confession. Quinn, however, continues to tail Zach, hoping to find something to prove his guilt.
Dexter's ApprenticeAs Quinn vets Zach, so does Dexter, eventually finding multiple images of Norma on a hard drive, which Zach took right after bludgeoning her. As Dexter sees Zach following his father in an apparent attempt to kill him, he quietly intercepts and puts the teenager on his table. Upon realizing that Zach is just like he once was (except without a guide), he decides not to kill him, but to take him on as his apprentice, teaching him The Code of Harry.
Eventually catching images of Quinn stalking him, Zach files a complaint to the police department and demands that Quinn back off, which he is ordered to do by Matthews and Batista. Zach is enthusiastic to go for a kill, but is told to have control over his urges for a while, so that things can go more smoothly. Eventually, he grows tired of Dexter holding him back and goes to his apartment, repeatedly knocking loudly on his door. Dexter's neighbor, Cassie, instantly notices this and tells Zach that he is not home, to which Zach gets even angrier and insults Dexter's attitude. Cassie is shown dead later on, and Zach's blood at the crime scene apparently points to him as the killer.
Shaun DeckerDexter, Knowing that he cannot simply have the police incriminate Zach since he knows too much about him, covers up the evidence pointing to the young man and searches for Zach himself, with the intention of killing him. Upon finding Zach, Dexter chastises him for allegedly having killed Cassie. However, he realizes soon afterwards that someone else tried to frame Zach for Cassie's murder (The Brain Surgeon) and that Zach was actually stalking a killer named Shaun Decker the whole time. After seeing Shaun's body, Dexter helps Zach cover his tracks and the two resume their relationship as teacher and student. This relationship is short-lived, however.
After Dexter returns home from a romantic encounter with Hannah McKay, he discovers Zach slumped back in his chair with his eyes open and motionless. A song is playing in the background from a phone, "Make Your Own Kind of Music", while Dexter approaches the body and spins the chair, revealing that the back of his head has been removed, with his brain cut open and a portion excised (the anterior insular cortex). Zach's body is then wrapped in black plastic, kept intact and dropped into the sea while Dexter is out on the Slice of Life. After Zach's death, Dexter resumes his hunt for Zach's killer and it isn't until episode 10 that, when Dexter is monitoring a man named Oliver Saxon's recent computer activity, he comes across a video of the latter murdering Zach with a bonesaw off-screen, proving that Saxon is none other than the true Brain Surgeon.
- Zach is officially Dexter's third apprentice, the first two being Miguel Prado (whom he later killed) and Lumen Pierce (who retired from killing).
- He may be the youngest psychopath on the series, next to Jeremy Downs.
- While Dexter feels he's nothing like Zach, they are fairly similar in physique and interests. Zach's appearance also somewhat mirrors Dexter's, though at a much younger age, and somewhat makes him like Peter Thornton, who became the "Dark Echo" of Dexter.
- Zach is one of the few characters dumped in the ocean who were not killed by Dexter or by anyone affiliated with him. The act of dumping him was to get rid of the body, avoiding another investigation into The Brain Surgeon and removing evidence of him being left at Dexter's house.
- He is the only apprentice of Dexter to be killed by the Main Antagonist (The Brain Surgeon).
- He is the only victim of The Brain Surgeon shown to be killed while he was still conscious. The other victims were first killed before their anterior insular cortex was removed postmortem.