"I need...to finish...this journey!"
Justin's mother died of cancer when he was ten years old, causing his father Raymond to stop going to church and begin drinking frequently, spiraling as a result. He also abused him and his older brother Todd, beating them whenever they received a grade less than an A in their schoolwork and also locking them in a shed for hours at a time. Todd would receive the worst of the abuse. The two brothers bonded over their shared love of Inferno, the first part of Divine Comedy (a 14th-century epic poem), which detailed the journey of its protagonist Dante through Hell while guided by the Roman poet Virgil. Eventually, in 1988, Todd, unable to take the abuse anymore, committed suicide by overdosing on pills, which led to Social Services taking Justin away from the custody of his father. In his adult life, he became an English teacher at a local high school and was strict with his students. One of his former students was Nathan Chow, who reminded him of Todd, which provoked a gradual psychotic reaction from him. The two struck a close friendship, with Nathan taking his classes twice, and when he graduated, Justin gave him a first-edition copy of Inferno. The two eventually decided to commit a series of Inferno-inspired killings when Nathan's life as a college student became miserable; they planned to end it in a double suicide based on the seventh circle, "Violence". On August 10, 2014, two months prior to "Burn", his father died from cardiac arrest and left the family home to him. Four days later, Justin began the killings, being set off by his father's death.
After claiming four lives in almost two months, Justin begins accelerating, abducting Michael Richmond one day after killing his latest victim, Joe Hazley. He takes him to the family shed, where he tries to drown him in a bathtub when he regains consciousness. However, Justin becomes distracted by hallucinations of voices chanting, "Abandon all hope, ye who enter here." When he halts his attack as a result, Michael rises from the water, to which he bludgeons him with a hammer, knocking him unconscious. He then proceeds to drown him. The BAU, called to investigate the killings and unaware of the first two victims, find the Roman numerals carved into the roofs of the victims' mouths and deduce from the numbers that there are more victims. Meanwhile, Justin begins construction on a wooden box, and remembers his attack on Michael as he continues hammering the nails into the wooden boards. Once he finishes the box, he abducts Alan Dorslawn, tortures him, and forces him inside it. The following night, Justin takes Alan to a secluded location. There, Alan tries to reason with him, but his pleas fall upon deaf ears as Justin closes the box shut. He then pours gasoline all over the box, as well as inside it through cracks in the boards, before setting it on fire, watching passively as Alan screams in pain. The next day, as they investigate Alan's crime scene, the BAU discover the presence of the first two victims as well, and Reid realizes that the unsub is recreating the nine circles of Hell in Inferno. Justin is next seen looking at childhood photos of him and Todd while inside the shed. He then stands up and approaches a handmade list of the nine circles, the first five of which are crossed out; he proceeds to cross out the sixth circle as well.
Soon afterward, he stalks a man named Connoley and his son and takes photographs of them as they are visiting a dental clinic. When Connoley complains about the money it cost to have his son's several cavities fixed, the boy claims he had been brushing his teeth, but Connoley doesn't believe him and angrily slaps him in the cheek. He then grounds him for two weeks and forbids him from going to a baseball game. Once Connoley drops off his son, Justin abducts and tortures him. He then goes to school to teach his classes. When one period is done, he is approached by one of his students, who asks about a B grade he received on one of his classwork. When Justin tells him it's the grade he got, the student replies that his father will "kill him" if he doesn't get an A. This provokes Justin to have a flashback to his childhood. When he remembers Todd's suicide, he crosses out the B on the boy's paper and replaces it with an A, which pleases the boy. Justin then returns to the family home, takes Connoley out at gunpoint, and shoves him inside a grave he dug, all the while projecting his father's image on him. When Connoley tries to reason with him, Justin, hallucinating his pleas as insults from Raymond, angrily beats him with a shovel. He then tries to shoot him, but Morgan and JJ arrive, telling him that there was nothing that could've been done for Todd now and that he couldn't let Raymond continue to affect him. This convinces Justin to surrender, and as he is arrested, he begins apologizing to his father. Considering his current mental condition and his unhealthy obsession with Inferno, Justin was institutionalized afterwards.
"Think this is painful?! Wait till you get to Hell!"
Justin targeted men of various races and aged in their mid-30s to early 40s, who were all surrogates for his father. All of them were strict with their young teenage sons (with the exception of Joe Hazley, who was instead a Big Brother volunteer and was strict with a boy he was mentoring), which he observed and took pictures of while stalking them.
Once the victims were alone in their cars on the road, he would bump into them as they drove into an intersection, which would make them want to pull over and walk out of their cars to see if there was any damage. At that point, he would incapacitate them by striking them in the head with a blunt object (presumably a hammer) and abduct them. The only exception to that was his first victim, Steve Oliver, whom he killed in his own apartment. His signature for the murders was torture by using a knife to carve Roman numerals in the roofs of the victims' mouths (which he forced open with a medical gag) in numerical order according to the nine circles of Hell described in Inferno. However, with Mr. Connoley, his seventh victim, he intentionally skipped over the seventh circle and had him represent the eighth circle, since Justin intended for himself and Nathan to represent the middle ring of the seventh circle.
Afterwards, he would take them to another location, usually located at or near the Leu family home, and kill them in various ways, all of which represented the punishments in the nine circles of Hell as described by Inferno with the exception of Dan Chen, whose body was covered in dirt post-mortem to represent the third circle "Gluttony" after being strangled since the manner in which he was killed did not represent the punishment. In the case of Michael Richmond, who was drowned to represent the punishment in the fifth circle, "Wrath", Justin was also forced to bludgeon him with a hammer when he fought back. When he tried to kill Mr. Connoley, he held him at gunpoint with a revolver, beat him with a shovel in a fit of rage, and tried to bury him alive to represent the punishment in the eighth circle, "Fraud". He later tried to shoot Connoley with the same revolver instead when his delusions grew increasingly worse. Depending on how Justin killed his victims, the bodies would either be left where they were killed or dumped off the sides of secluded roads.
The unsub is a male between the ages of 35 and 40 who is killing parental figures based on his need for revenge and punishment. He has designed his M.O. to recreate the nine circles of Hell in Inferno, which describes the sinners encountered in each circle of hell and the punishments they had endured. The unsub has killed all the way to the sixth circle and marked his victims accordingly with a Roman numeral on the roofs of the mouths. However, since his victims did not commit the sins associated with each circle, it is probable that the killings are symbolic of a father figure who abused him in the past.
In Inferno, Dante traveled with the Roman poet Virgil, who assured him that he would enter paradise if he completed his journey. Consequently, the unsub is likely metaphorically taking this journey with someone else, likely a sibling who suffered the same fate at the hands of an abusive father (later revealed to be a literal journey with his accomplice and former student Nathan). Considering his fascination with Inferno, the unsub may be an academic. He is patient, stalking his victims and, after watching them discipline a child harshly, waiting until what he considers the appropriate moment to abduct and kill them. He will continue with the final three circles of Hell until he feels completely avenged.
- August 14: Steve Oliver (carved the Roman numeral "I" into his mouth, then tied to a chair, gagged, and asphyxiated with gas from an oven in his apartment; represented the first circle, "Limbo")
- September 3: Kyle Dern (carved the Roman numeral "II" into his mouth, then tied to a fence and electrocuted; represented the second circle, "Lust")
- September 23: Dan Chen (carved the Roman numeral "III" into his mouth, then strangled and covered with dirt post-mortem; represented the third circle, "Gluttony")
- October 6: Joe Hazley (carved the Roman numeral "IV" into his mouth, then run over with a car and fatally crushed; represented the fourth circle, "Greed")
- October 7: Michael Richmond (carved the Roman numeral "V" into his mouth, then bludgeoned with a hammer and fatally drowned in a bathtub; represented the fifth circle, "Wrath")
- October 7-8: Alan Dorslawn (carved the Roman numeral "VI" into his mouth, then burned alive in a box; represented the sixth circle, "Heresy")
- October 8: Connoley (first name unrevealed; abducted, carved the Roman numeral "VIII" into his mouth, beaten with a shovel, held at gunpoint, and attempted to bury alive, then shoot; was rescued; represented the eighth circle, "Fraud")
- Note: There were also two other circles that have not been attempted by Justin: the seventh circle, "Violence"; and the ninth circle, "Treachery". Since both Justin and Nathan had intended to commit suicide to represent the seventh circle, it is possible Justin had another target in mind for the ninth circle, possibly the father of the student who had asked Justin to give him an A for his assignment.
- C.S. Lee, the actor who portrays Justin, previously portrayed Vince Masuka, a lead forensics investigator featured in the popular drama series Dexter, which centers around a vigilante serial killer.
- Justin is based on a number of unsubs in the show's history, being tied with Kevin Decker for having the most inspirations out of any other unsub (with a total of seventeen). They are:
- Season Two criminal Tobias Hankel. Both were psychotic serial killers and abductors who were abused by their fathers, had a varying M.O. and a religious aspect to their killings, and attempted to kill their would-be victims by burying them alive.
- Season Three serial killer Stanley Howard, who also intentionally killed his victims in various ways in accordance to an aspect of their lives that affected them (in Stanley's case, one's greatest fear), burned one victim alive, drowned another victim, trapped yet another victim inside a box that was instrumental to their deaths (Stanley suffocated his inside the box, while Justin burned the victim alive while the latter was inside), were also abused by a parental figure in their childhoods, began killing as a result of the natural deaths of their abusers, and tried to kill their last victims by burying them alive. Also, the scene where Justin's delusions cause him to see his would-be victim as his father is similar to the scene where Stanley projects his mother's image onto his wife while arguing with her.
- Season Three serial killer Gary. Both were victimized as children by parental figures (Justin was abused by his father, while Gary was abused by his foster mother), had a varying M.O., used blunt objects on most of their victims, used a ruse on their victims before attacking them, committed crimes that were initially undetected by the BAU and local authorities (Justin committed two murders; Gary committed four victimless home invasions), and targeted individuals who represented the sources of their rage after seeing their interactions with children, which they perceived as being abusive (though Gary's first two victims were actually abusing their daughter).
- Season Three criminal Peter Redding. Both were serial killers who devolved, had a varying M.O. (which included asphyxiation), had brothers who were abused by their fathers, and their triggers were someone's death (for Justin, it was the death of his father, for Peter, it was the deaths of the children of who died in a recreation center fire). Also, Justin's brother committing suicide to avoid his father's abuse, seems to be an allusion to Peter's murder of his brother to help him avoid their father's abuse, making the death look like a suicide afterwards.
- Season Four criminal Adam Jackson. Both were psychotic serial killers who were abused by paternal figures after their mothers died, targeted men who were surrogates for their abusers, and had ante-mortem rituals that involved doing something to their victims before killing them (Justin tortured his victims; Adam raped his victims).
- Season Six criminal Hollis Walker. Both were serial killers who had a varying M.O., used blunt objects on at least some of their victims, had fathers who abused them and mothers who died during their childhoods, held academic professions, and befriended teenage boys who became involved in their killings in some way.
- Season Eight criminal Adam Rain. Both were psychotic serial killers who were motivated to commit their crimes by the deaths of their fathers, had a varying M.O., abducted their victims after using a ruse on them, tortured their victims in some particular way (Justin carved Roman numerals into the roofs of his victims' mouths, while Adam dislocated his victims' limbs as well as boring holes into their hands and feet), and would be institutionalized after they were arrested.
- Season Eight criminal Rodney Harris. Both were psychotic killers who were abused in their childhood in some way and targeted individuals who represented the sources of their rage after seeing their interactions with children, which they perceived as being abusive.
- Season Nine criminal Leland Duncan. Both were psychotic serial killers whose murders were motivated by the deaths of their at least one of their relatives (for Justin it was his father; and for Leland, it was his adoptive parents), had a varying M.O., killed their victims in ways that were based on and viewed as punishments, would stalk and take pictures of their victims, had signatures that involved torturing their victims in some particular way (Justin carved Roman numerals into the roofs of his victims' mouths, while Leland branded the seal of his ancestor on his victim's necks and non-fatally slashed their arms), committed at least one murder that was initially undetected by the BAU and local police, and believed they were sending their victims to Hell.
- Justin's various methods of killing his victims are similar to many previous serial killers who have appeared on the show:
- Peter Redding killed his fourth victim by asphyxiating him with gas in his residence.
- Wade Hatchett and Alan Anderson killed their victims by strangling them and dumping their bodies on the sides of roads.
- Ian Coakley ran his victims over with a car.
- Chase Whitaker killed his first and fifth victims by drowning them after first striking them with a blunt object (Michael Richmond, who was subjected to this particular method of killing, was also Justin's fifth victim), and he also killed his second victim by strangulation.
- Mark Gregory and Johnny Ray Covey drowned their victims in bathtubs after torturing them.
- Kaman Scott burned his victims alive in a specific ritual.
- A photo of Justin seen on Kevin Lynch's computer shows that his Social Security number is 981-00-1138.