Hollis was born to a Caucasian father, Hollis Walker, Sr., and an unnamed African-American mother. The senior Hollis was an expert on indigenous African religions and wrote a total of ten books about the subject. He was also highly physically abusive towards his son. When Hollis was twelve years old, his preparatory school did a psychological evaluation of him, which came back with worrying results. His mother committed suicide shortly after he was sent to boarding school. After that, Hollis stayed at school all of the time, even during the holidays and vacations. Because his father didn't care about him, he didn't bring him back into the house. During adulthood, Hollis got a job as a college professor and wrote a book about Palo Mayombe, a secretive, death-related Afro-Caribbean religion; the book received a negative review written by his father, which was shown in a newspaper article.
When he became eligible for tenure at the college where he taught, Hollis began a plan to commit a series of murders to kill people using the religions he researched in order for his academic work to gain fame and for him to be noticed by his father. In order to prevent himself from being caught, he planned to frame a delinquent teenage boy named Elian Morales by leaving evidence behind at the crime scenes and at Elian's home to make it appear that he was responsible. He befriended Morales, who at the time was angry with a man he looked up to, Julio Ruiz, and wanted another father figure. On January 11, 2011, the day after Morales was released from jail, Hollis killed a vagrant named Eduardo Guzman. Within the next week, he killed two more victims, leading to the BAU being called in.
Hollis is first seen following Jimmy Mercado and his pet dog home. When Mercado is about to approach his home, Hollis subdues him with a metal pipe. He then tortures and kills him as well as his dog. The next day, he is interviewed about lesser-known religions by Reid and Morgan, who are unaware he is actually the unsub. They show him some crime scene photos and detail the mutilations the unsub carried out on the bodies, such as cutting the victim's tongue out and putting it in a dish, and cutting off the head, extracting the brain and leaving the rest of it behind. Hollis informs the agents about the religions used in the murders, including Palo Mayombe, and what the unsub could be planning to do. The two then leave after learning about Mercado's murder. Hollis later decides to execute an endgame, tracking down Morales at a soup kitchen and holding him captive, with the intention of murdering him via heroin overdose in order to trick the authorities into believing he committed suicide to escape incarceration.
However, his plan is ruined when Ruiz arrives in search of Elian. Hollis is forced to take Ruiz captive as well, taking the both of them to the abandoned house next to the building, which is Ruiz's old foster home. When the BAU realize that Ruiz and Morales are missing, Reid realizes they are in the abandoned house and gains entry, only to be held at gunpoint by Hollis. The rest of the team realize that Hollis is the unsub as he, a leading expert in the religions used by the unsub, didn't remark that some of the mutilations didn't fit with the traditional characteristics of said religions. At the house, Reid tries to talk Hollis down, remarking that in order for his plan to work, he needs to get caught or his involvement will never be known. Suddenly, Reid starts suffering from a headache, and that, plus Ruiz's incessant moaning towards Hollis, agitates Hollis and distracts him long enough for Reid to knock him out. The rest of the team arrives and arrests Hollis, who asks if his father will find out about what he has done. Reid later lies to Hotch that he pretended to have a headache.
Hollis's string of killings were based on several Afro-Caribbean religions, primarily Santería and unbaptized Palo Mayombe. His first three victims were all middle-aged African-American and Hispanic people of both genders who came from the lower classes of society and went to the soup kitchen where Julio Ruiz and Elian Morales volunteered at. This choice of location was made to make the authorities believe it was where Julio found his victims.
The first victim, Eduardo Guzman, was killed in an alleyway, while the victims afterward died in their homes. Hollis would meet them at the kitchen, create a relationship with them, and, when they wanted to, start out by performing a ritual with them (their participation being consensual, as they did not know they were about to die), which involved drawing a circle-like symbol on the floor, decapitating a pigeon, and scattering its blood and feathers all over the scene. He also turned any crosses in the room upside-down, even placing one on Yarina Espinal's body after killing her. He would then murder the victims from behind during a vulnerable moment in various ways, cut off their fingers or their whole hands post-mortem and took them with him, wipe any blood that was on their faces, posed the bodies face-up on the floor (with the exception of Yarina Espinal, whose body was posed on her bed), and placed cowrie shells in their mouths and eyes as a way of symbolically silencing his father through them.
His fourth victim (who also went to the soup kitchen Ruiz and Elian volunteered at) was subdued with a metal pipe in his home, dragged to the kitchen, tied to a chair and table with duct tape, and had his mouth covered with the same duct tape. His hands and tongue were removed (presumably with a machete) to torture him, then killed by decapitation with the same machete, and his brain was removed and taken, along with his hands, afterwards. His tongue and head were left in his home and placed in dishes, the latter being put in a cabinet, all of which are not part of any ritual. During the third and fourth murders, he also decapitated the victims' house pets, a cat and a dog respectively, and placed their heads near the victims.
His killings were meant to look like ritualistic murders so that he would achieve fame for his academic work and could frame Elian Morales for committing them afterwards; in order to make Elian look responsible, Hollis wore his shoes and left bloody footprints at the crime scenes, and also placed the body parts he took from his victims, along with chalk drawings and drugs, among his belongings. When he attempted to kill Elian, he abducted him and injected him with heroin to make authorities believe he died from a drug overdose to avoid being incarcerated. When he attempted to kill Julio (who was targeted incidentally), he also abducted him, tied his arms and legs together, covered his mouth with duct tape, attempted to shoot him with the same revolver used to kill the first victim, and intended to cover up his death as being committed by Elian in a drug-maddened, devolving state. He also held Reid at gunpoint with the same revolver, intended to shoot him as well, and hoped to cover up his death as another incidental murder by Elian.
The unsub is a male who is working alone, as there is no evidence to suggest the presence of more than one offender at each of the crime scenes. Though he is behaviorally 17 to 22 years old, he may be much older. He has most likely served time in some kind of prison or institution, which stunts emotional growth. He is now part of the community, most likely Hispanic or African-American. He has most likely been abused as a child and has been in the juvenile system or in foster care, and the age of his victims suggests that he may be taking some sort of revenge against parental figures. The religions that played a part in his killings are primarily Santería and Palo Mayombe; as a result, he may have a religious connection to the victims, likely being a practitioner who people trust and rely on for healing. Since he targets people who are fragile and vulnerable, whom he builds relationships with, he also has close access to his victims and may therefore work at a government-issued aid office or community center. His coworkers would describe him as being moody and having flashes of temper. He is highly organized in his planning, but allows his urges to take over when he kills. This type of behavior suggests that, even though he thinks he has an objective goal, he is instead being primarily driven by a compulsion to kill. His psychopathic hubris and the success of his murders makes him feel invincible, which subsequently sparks a rapid escalation in his M.O. and his time-frame. As a result, this makes him more efficient and violent, and therefore also increasingly unpredictable and dangerous.
The unsub is also framing Elian Morales for his killings. He is someone who is intelligent and controlled enough to set up a convincing trail of false evidence for the authorities to find. He is also someone investigators have met and has probably even followed the investigation all along. He began his murders for gain of some sort, likely attention from the media for not the murders, but the religion. However, his enjoyment of killing is disrupting the organization he planned for the crimes.
Hollis may have been inspired by Adolfo Constanzo, a Cuban-American serial killer, drug dealer, and cult leader from Miami who killed over 25 people in ritualistic manners, using Voodoo, Santería, and Palo Mayombe (the same religions that Hollis based his murders on) as the basis of his murders. It is believed that Constanzo tortured and murdered his victims to ensure his success as a drug dealer.
Hollis is also similar to Richard Ramirez, a.k.a. "The Night Stalker". Both were serial killers who were the children of interracial married couples; had a varying M.O. and religious aspects involved in their crimes; would kill their victims in their homes; and used revolvers, machetes, and blunt objects on their victims (though Ramirez also used other weapons).
Hollis is also partially similar to Charles Ng. Both were serial killers who were abused by their fathers and later sent to boarding school by them.
- January 11: Eduardo Guzman (shot with a revolver; sawed one of his fingers off post-mortem and took it)
- January 15: Yanira Espinal (bludgeoned with a pipe; cut one of her fingers off post-mortem and took it like the previous victim)
- January 17: Victor Cabrera (slashed in the neck and right arm with a machete; cut both of his hands off post-mortem and took them; his cat was also killed)
- January 18: Jimmy Mercado (subdued with a pipe, tied up, cut both of his hands and his tongue off, decapitated with a machete, removed his brain post-mortem, and took it; his dog was also killed)
- January 19: The standoff at Ruiz's abandoned foster home:
- Chris Butler, the actor who portrays Hollis, previously appeared on Criminal Minds, playing a different role in the Season One episode The Popular Kids; in the episode, he starred as Deputy Harris, who is one of the investigators assisting the BAU during the prominent case, which also involved a series of ritualistic murders that were made to look like the work of someone else.