"Did you see it? The darkness? The light? Did you see?"
Chase was born on May 9, 1980, in Ridge Canyon, California. His father, Daniel, was an abusive alcoholic whose wife, and Chase's mother, left the family, leaving Chase to live with Daniel in a cabin by Ridge Canyon Lake. On October 28, 1990, at the age of ten, he was diagnosed with lymphoma (a kind of cancer), but it went into remission on June 9, 1992, when he was twelve. On February 6, 1996, when he was sixteen years old, he and his father were fishing in the lake from a jetty. When Chase started talking back at his father, he forced Chase to take his shirt off and whipped him with his belt, a usual punishment. When he was done, Chase argued with him again, and as a result, Daniel punched him in the face so hard that he fell into the lake and nearly drowned. His father dragged him up and tried to revive him but couldn't. Thinking Chase was dead, he dragged him into the woods and buried him. Shortly afterwards, Chase woke up inside the grave and dug himself up. Upon coming back to the cabin, he struck his father in the head with a shovel, dragged him to the lake, and drowned him. He was eventually somehow arrested by police and institutionalized for the murder, but was released at the age of eighteen.
On September 2, 2011, Chase was diagnosed with fourth-stage lymphoma and learned that he only had three months to live. He became interested in a news story about Jake Shepherd, a hoodlum who had turned his life around and become religious after suffering an ATV accident; while in an ER, he flatlined for four minutes before being resuscitated, during which he claimed to see an angelic figure who told him it "wasn't his time". When Shepherd was at Ridge Canyon Lake to be baptized by his congregation, Chase approached him, hoping to learn from him what dying was like. When Shepherd didn't give him the answers he wanted, he wound up killing him by strangling and drowning him, unsuccessfully trying to revive him. After that murder, Chase became a serial killer, non-fatally drowning people in the lake and bringing them back to life to ask them what it felt like before finally drowning them fatally. He initially targeted men with the same kind of physicality of being well-built with dark hair (presumably because they reminded him of his father), but as his lymphoma grew worse to the point where coughing fits would briefly distract him, Chase started looking at other victims to prey on.
Chase is first seen spying on Nick Scirvin, who is out camping with his friends. When Nick's friends go out onto the lake, isolating him, Chase moves in. Meanwhile, Nick's brother, Phinny, tells him via walkie-talkie that local authorities have found some of Chase's previous victims in the lake, just before he spots Chase sneaking up on Nick. Unfortunately, it is too late for Phinny to warn Nick, and Chase knocks him out before dragging his body away. Simultaneous to the BAU being briefed about his case, Chase proceeds to drown Nick and puts his body in Lake Banter instead of Ridge Canyon Lake. Later that day, he spies on Lacey Campbell and her friends before pumping some of the gas out of her jetski. Later, he watches as she races with her friends, only to run out of gas midway through the race, and she drags her jetski to the shore. Approaching her, Chase introduces himself and offers to ride Lacey back to town, to which Lacey turns down the offer. However, Chase counters with the recent story of his victims being discovered, and Lacey changes her mind and goes with him. He later proceeds to drown her, but the drowning accidentally becomes fatal, and despite Chase's desperate attempts to resuscitation, she dies. At his home, Chase begins coughing out blood at the bathroom sink and takes his medication.
Later, he approaches Samantha Braun, whose car has broken down in the middle of the road, and she tells him that her son Evan is waiting at the car. Chase knocks her out before approaching Evan, luring him in with the story that his mother had been in an accident. Meanwhile, the BAU realize that he is suffering from lymphoma as well as why he kills his victims. At the harbor owned by Daniel, when he is unable to get an appropriate response from Samantha after non-fatally drowning her, Chase proceeds to do the same to Evan. However, Chase gets distracted from his coughing, and Evan uses the opportunity to cut his bonds, escape, and pull Chase into the water. Evan then runs away from the harbor with Chase in pursuit, all the while coughing. After a lengthy chase, Chase manages to catch up with Evan at another part of the lake and attempt to drown him again, but the BAU arrive and convince Chase to release Evan before diving beneath the lake with the intention of drowning himself. However, visions of Daniel and a younger Chase appear to him, the former telling him that "it's not his time". Chase is then resuscitated by Prentiss and Reid, Prentiss telling him that it's not his time. Though he is last seen alive, it can be assumed he died of his lymphoma while incarcerated.
Chase initially targeted heavy-built Caucasian males with dark hair who likely reminded him of his father. However, because his lymphoma was worsening, he later started killing more frequently and targeted random victims, even attempting to kill more than one simultaneously. After approaching them with some kind of ruse, he would lure them away from whoever they were with, bring them over and restrain their wrists to a dock in an isolated part of Ridge Canyon Lake, and drown them in it. When they passed out, he would pull them out of the lake, revive them with CPR (his signature), and ask them what it was like while they were unconscious. Inevitably, they would be killed after repeated instances of drowning, after which he tied rocks to them and dumped them in the lake, allowing said rocks to weigh them down.
After his murder of Nick Scirvin, he stopped weighing them down and even left Nick's body in a different lake as a forensic countermeasure and due to the authorities finding where he initially dumped his victims. As his killings progressed, he would take more time drowning them, hoping they would experience more of the "other side", and revive them more frequently. He also started killing them in colder parts of the lake in order to keep them alive longer. His first victim, his father Daniel, was first struck with a shovel before being abducted and drowned. His second victim Jake Shepherd was fatally strangled on accident, most likely in a fit of rage, then drowned and given CPR post-mortem, since Chase believed the strangulation didn't kill him. In addition, Nick Scirvin wasn't lured in with a ruse, being struck in the head with a stick and incapacitated instead.
The unsub is a white male aged in his mid-to late-20s who is a local to the area. He dumped Nick Scirvin's body in the lake and was compelled to then circle back towards Ridge Canyon. He somehow went from choking and carrying fit men to their watery graves to drowning physically smaller victims unceremoniously. Diatom levels indicate he has stopped moving his victims altogether. Because of the changes to his behavior, he has most likely been injured or sick. He has experience in performing CPR, so he may be a doctor, lifeguard, or anyone else with training in resuscitation. Ridge Canyon Lake means something to him and he may have committed at least one murder there before. He may work in local law enforcement or as a park official. He has accelerated his attack schedule, and he will not wait long to strike again.
At first, the unsub was believed to be a sadist with a God complex, who would get off on nearly murdering his victims repeatedly and that it was extremely vital that he brought them back from the dead. As a result, Reid compared him to Rodney Alcala, who would have a habit of resuscitating his victims after strangling them to the point of unconsciousness, then strangling them again. It later turned out that he was actually motivated by a fear of not knowing what to expect of life after death, being so close to dying himself.
- February 6, 1996: Daniel Whitaker (his father; struck in the head with a shovel, then drowned once)
- October 16: Jake Shepherd (fatally strangled him on accident, then drowned post-mortem)
- October 20: Kirk Huggins (was repeatedly drowned)
- October 23: Ben Ganzman (was repeatedly drowned like the previous victim)
- October 25:
- Nick Skirvin (incapacitated with blunt-force trauma using a stick, then repeatedly drowned; his body wasn't weighed down; was left in another lake)
- Lacey Campbell (was drowned once and unsuccessfully revived)
- October 26: Samantha Braun and her son Evan (abducted and attempted to kill; both were rescued):
- Samantha Braun (knocked out and non-fatally drowned at least twice)
- Evan Braun (attempted to non-fatally drown; later assaulted and held at knifepoint)
- Chase is very similar to Season One criminal Mark Gregory. Both were serial-turned-spree killers who killed their victims by drowning them, and killed one of their parents as their first victims when they were children (Chase killed his father, while Mark killed his mother).
- Chase also bears similarities to Season Three criminal Joe Smith. Both were serial killers who devolved, learned that they were dying of a disease (Joe had a brain tumor; Chase had lymphoma), which would be one of the reasons they started killing; and killed victims who were presumably surrogates for someone in their lives (Joe targeted women who were presumably surrogates for his ex-wife; Chase's second to fourth victims were presumably surrogates for his father).
- Drew Osborne, the actor who portrays the young Chase, previously starred as killer Peter Lidge in an episode of Suspect Behavior, the short-lived Criminal Minds spin-off.