"They don't understand, I'm trying to help. If they would just do their jobs, I wouldn't need to do it for them."
In 2012, Danny was diagnosed with severe paranoid schizophrenia, which was inherited from his mother Miriam, also a schizophrenic, who worked as a landlady. One of Miriam's tenants was Patricia Valdez, whose ex-husband David Ruiz was a known criminal. On April 2014, Miriam was killed by a burglar, and Danny blamed Ruiz for committing the murder. Without Miriam, who influenced him in taking his medication, he put it off, began drinking, and lost his driver's license. He went into a downwards spiral that intensified when he couldn't find Ruiz, who had actually been incarcerated in San Diego for an armed robbery he committed on February 28 earlier that year. Unaware of this, Danny instead abducted Patricia and her daughter Milena and killed the both of them. Afterwards, he remorsefully buried their bodies in the front yard of his home. He then began hallucinating visions of Patricia and Milena, who would encourage him to go out and find Ruiz to avenge his mother's murder, all the while killing any other person he comes across and believes to be committing an immoral act. Eight days later, Danny was driven to kill Gary Fisher, a john who was soliciting a prostitute. Three days later, he killed another john, Nate Cochran, as well as a prostitute he was soliciting, named Tasha Brooks.
Immediately after killing Cochran and Brooks, Danny flees back to the apartment, escaping two police officers on his trail. He is met by the visions of Patricia and Milena, who see the fresh blood still on him and clean it off from him. The next day, Danny experiences a painful headache brought by his schizophrenia as he is drinking. Moments later, Milena comes to him and begins massaging his head. The two begin talking, and Danny confides in her that he still misses his mother. Milena then encourages him, saying that he needs to find Ruiz and that the entire world needs protection, before Danny's headache worsens, causing him to scream. The following night, he continues drinking, which Patricia scolds him for doing despite Milena's words of support. Patricia then expresses her worry about him, but he counters that he is still looking for Ruiz and that he had to do something about his victims. He then promises a concerned Patricia that he will be careful in the future.
Afterwards, he goes out and eventually wanders underneath a bridge, where he hears screaming. Venturing further into the bridge, Danny finds a local drug dealer and car thief, Lamar Taylor, trying to take the purse of an elderly woman named Clara Miller. He empties out an entire magazine on Lamar, killing him, and then approaches Clara, who he notices is moaning and clutching her chest. When he asks her if she is all right, she collapses and dies of a heart attack despite his protests. Enraged at this, Danny stands over Lamar's body and blames him for Clara's death, saying that "[he's] just like him" before proceeding to beat the corpse. However, it is revealed during the next morning that Clara was Lamar's former schoolteacher, who changed his criminal ways and became his friend, meaning Danny was hallucinating Lamar trying to mug Clara. Following the bridge shooting, Danny, Patricia, and Milena look at a photo of Miriam before Danny begins blaming Patricia for his mother's death and that she should have been the one to die, causing her to storm out. Guilty over his words, he then remarks that "it should've been [him]", to which Milena tells him if he was shot, there would be no one to protect her and her mother.
In an effort to reconcile with Patricia, Danny cleans up the room, and when Patricia returns, he gives her a bouquet of roses, stating they made her eyes look even more beautiful. After she forgives him, she tries to leave for work, but Danny protests that Ruiz might come back for her. When Patricia replies she needs the job, he states that she doesn't have to pay the rent for the apartment and that his job salary will be enough to support all three of them. Appeased, Patricia kisses him, thanks him, and leaves. Right afterward, Danny and Milena see a press conference by JJ concerning the former's killing spree, and Danny chastises the authorities for not understanding and not doing their jobs. He then leaves for the night and wanders to a nightclub, where he stumbles across Christopher DeLuca and his girlfriend Lindsey Cooper having sex in a nearby alley, although he hallucinates it as a rape by Christopher. He assaults Christopher and then, at what he hallucinates as Lindsey's urging, shoots him repeatedly, killing him as Lindsey flees in a panic. Interrogations with Lindsey later gives the BAU a composite sketch of the unsub, as well as their deduction that he is a schizophrenic.
Returning home, a bloodstained Danny is confronted by a police officer, who notices the bloodstains on him, prompting Danny to kill him. Patricia sees the man's body and confirms he is actually a mailman. When she urges Danny that they should go to the police, he refuses and forces her back inside the home at gunpoint. Meanwhile, the BAU identify Danny as the unsub, and Morgan, JJ, Reid, and a local detective arrive at the home, finding the mailman's body. They enter and hear Danny yelling at Patricia and Milena in his apartment room, though they realize he appears to be the only one inside. When Morgan tries to get him to come out, Danny fires several times through the closed door, screaming that he has hostages. Morgan and JJ appeal to Danny and confirm Ruiz's whereabouts. When he remains defiant, he begins hallucinating about all of his victims, who taunt him and try to convince him to commit suicide. However, at Patricia and Milena's urging, he surrenders instead. When JJ asks where Patricia and Milena really are, Danny points them to a makeshift grave outside the home. As he is taken into custody, he looks upon the grave as it is being dug up by officers, exposing Patricia and Milena's decomposed bodies. When he looks up, he sees visions of them bidding him farewell and smiles happily.
Danny targeted people he believed were committing immoral acts, although the only victims who were actually doing so were Tasha Brooks and the johns, while the rest of the victims were killed after he hallucinated them committing crimes. He would find most of his victims while patrolling the streets at night and shoot the victims repeatedly in the chest, neck, and head (mostly in the face) with a .45-caliber Heckler & Koch USP handgun, emptying at least one magazine on them. He would also beat some of his victims savagely before or after killing them. He killed his victims in neighborhoods that were impoverished and had high crime rates, but in the case of Christopher DeLuca, he was killed in a gentrified neighborhood with a low crime rate. After abducting and killing Patricia and Milena Valdez, Ruiz's ex-wife and daughter, respectively, he buried their bodies in the backyard of his home out of remorse, something he didn't do for his later victims as he was in the midst of a psychotic break during those killings.
"You stay out of my city!"
The unsub is a white male aged in his 20s and a "moral enforcer", a type of vigilante. He is mission-oriented and may believe it is his duty to clean up crime on the streets. He likely does nightly patrols and stalks anyone that he thinks is suspicious. His post-mortem beating of Lamar Taylor is connected to his extreme level of anger. He may be suffering from some kind of drug-related psychosis, and it is also believed he may have been a victim of violent crime himself. The crimes appear to be personal, which makes him even more unpredictable and dangerous. He is gaining confidence with every murder, and as his confidence grows, so will his belief in his cause. The unsub lives in the Los Angeles area and possibly grew up there, but it is believed he is severely antisocial to the point where he probably cannot keep anything more than a part-time job. According to statistics, the unsub will likely not be arrested at the end of the investigation, as with the vast majority of these types of serial crimes, the killer usually does not go down easily and is not apprehended alive. So far, he has been smart enough to flee before the authorities show up. Even though he is a vigilante, he may think the authorities do not share his belief in punishing criminals, and his zeal may be connected to a deep mistrust in law enforcement.
- April 17: Patricia Valdez and her daughter Milena (David Ruiz's ex-wife and daughter, respectively; both abducted and killed, presumably by shooting)
- April 25: Gary Fisher (a john; beaten and shot thirteen times in the head and chest)
- April 28: Nate Cochran and Tasha Brooks (a john and prostitute, respectively; both shot thirteen times each in the chest, neck, and head)
- April 29: The bridge shooting:
- Lamar Taylor (shot thirteen times in the back and beaten post-mortem after hallucinating him mugging Clara Miller)
- Clara Miller (Lamar Taylor's former teacher; indirectly died from a heart attack as a result of the trauma of the shooting)
- April 30: Christopher DeLuca (pistol-whipped, beaten, and shot thirteen times in the head and torso after hallucinating him raping his girlfriend)
- May 1: The Stokes home shooting:
- Danny seems to be similar to a few unsubs in the show's past:
- Season One criminal Marvin Doyle. Both were schizophrenic vigilante serial killers, had at least one parent who was killed in a robbery, which were their stressors, would kill their victims at night (although Danny killed his last victim and presumably his first two victims during the daytime hours) and had M.O.s that involved shooting their victims (Marvin shot his victims to subdue them, while Danny fatally shot his victims).
- Season Three criminal Jonny McHale. Both were psychotic vigilante serial killers who devolved into spree killers, had stressors that involved the murder of a loved one (for Danny, it was his mother; for Johnny, it was his fiancé), would kill their victims at night (although Danny also killed at least one person during the daytime hours), performed overkill on their victims, and abducted and killed at least one victim (who was personally connected to the murders of their loved ones in some way).
- Season Four criminal Norman Hill. Both were psychotic spree killers whose murders were motivated by the deaths of a close female relative, killed their victims by shooting them, committed a double homicide in which they repeatedly shot two victims seated in a car until they emptied out their magazines, committed their murders in California, were haunted constantly by hallucinations of their first victims, and killed their later victims after hallucinating them doing certain actions that they were not actually doing.
- Season Six criminal Ben Foster. Both were schizophrenic spree killers who killed their victims at night, performed brutal overkill, were disorganized during their murders, committed at least two murders (which were also their very first) that were initially undetected by the BAU and local police, and saw hallucinations of their victims (although in Ben's case, he only saw the victims he killed as a child).
- Season Nine criminal Wallace Hines. Both were psychotic serial killers who devolved, killed their victims by shooting, usually killed their victims at night, and were haunted constantly by hallucinations of their first victims, who they were also associated with in some way.
- Season Nine criminal Clifford Walsh. Both were spree killer vigilantes whose stressors were the deaths of family members killed in robberies, killed their victims by shooting them, performed overkill on at least one of their victims, and committed their killings when they could not exact revenge on the sources of their rage.
- Some scenes in the episode show Danny firing fourteen to as nearly as twenty-five gunshots from his gun without reloading, although a Heckler & Koch USP (the type of gun he uses) is only capable of holding a maximum of thirteen rounds, including one in the chamber (as stated by Reid). These are likely errors on the part of the writer and the editor.