|“||Wives wither... children perish... but me? I'm an excellent father.||”|
— Arnold during his interrogation with Morgan in "The Fox"
Arnold's father physically and sexually abused him as a child, something which caused him to develop a strong sense of self-hatred. He later got married to a woman named Fay, with whom he fathered a son and daughter named Karl Jr. and Sarah. He was very controlling, bordering on obsessive-compulsive, which resulted in a divorce about five years prior to the episode in which Fay won full custody of their children. After that, Arnold took some time off from his job as a family psychologist, became unfocused, and started drinking heavily. He began infiltrating the homes of families he was treating, took them hostage, and pretended to be their father before killing them.
After killing eight families, the BAU is called in to investigate, but they only believed they were investigating the deaths of two families, the Millers, and the Crawfords, as the rest of the families' deaths were apparently unconnected. After tracking him down, Morgan and Gideon followed him into the basement of the Dunken's house, where he used the Dunken's baby as leverage. Arnold eventually handed over the baby before making an attempt to escape, but Morgan, an expert in martial arts and a judo black-belt got the better of him and threatened to break his neck if he even moved. Back at the BAU headquarters, the team tricked him into confessing by switching the places of two crime scene photos on a board. Since Arnold couldn't stand anything being out of place, he had an outburst, accidentally confessing to having detailed knowledge of the murders. When Hotch searched his office, he found a box containing eight wedding rings, including those of the Miller and Crawford families.
"Once I killed the children, it always amazed me how little the father fought the inevitable."
"Which was what?"
According to Arnold, after his murders became public knowledge, he gained a number of fans, some of which even made a website dedicated to him. In the episode, a spree killer targeting entire families becomes active in Hampton, Virginia. Hotch and Prentiss interview Arnold at the Red Onion State Prison, where he assists in their investigation after receiving envelopes containing newspaper clippings about the murders which appear to have been mailed by the killer. During this, he comments on Prentiss in inappropriate ways, causing Hotch to agree to have Prentiss interrogate him alone, where she begins "flirting" with Arnold to get info. Despite Prentiss discovering that the unsub is a female, Arnold continues to refer to his admirer as "he", and when Hotch tells him that he is done with him, Arnold reveals the admirer said the same thing. Hotch then takes the journal where Arnold kept all of the newspaper clippings he received. Inside, he finds a newspaper clipping about himself, signed with the Eye of Providence, revealing that it was George Foyet who was sending the clippings to Arnold, a fact Arnold was aware of, and that Foyet was using him to get a message to Hotch. As Hotch left, Arnold laughed in delight at his despair.
The unsub is a white male in his 40s. Organized killers like this unsub are typically skilled workers with above-average intelligence, a high birth status, and are often male. He is socially confident in his workplace and sexually confident with women. He is also meticulous with his crimes, and everything has to be in its proper place. Every one of his familicides is pre-planned; to him, targeting the victims is almost as pleasurable as it is actually killing them. He also does extensive research about his victims, such as when the kids come home from school when the father comes home from work, and when dinner is ready. He keeps all of the acquired information in a book or journal to ensure that nothing is left to chance, and he takes a lot of time to make up a good strategy plan before killing them. He specifically targets families because he has lost his own.
According to Hotch and Prentiss in his last appearance, Arnold was also sexually motivated, as a result of the sexual and physical abuse he suffered at the hands of his father. This abuse caused him to suffer from extreme self-hatred, which evolved into his willingness to kill fathers as surrogates for his own father and himself.
"... And I watched them, for a number of days, always at night. Saw how they lived, how they loved. I would keep them apart, until the last night, until the last supper. Then I would bring them, one by one, down to the basement, the youngest first, father last."
Arnold targeted families he viewed as dysfunctional; the named victims he first encountered in his work as a therapist (with the exception of the Dunken family, who were seeing another therapist). The named families consisted of a father (or stepfather, as in the case of the Miller family), a mother, an older son, and a younger daughter, which was meant to be a resemblance to his own family (with the exception of the Dunken family, which had an older daughter and an infant son). He would stalk them for weeks and watch them at night while they were inside their homes. He would strike his victims when they were supposed to be on vacation, ensuring that nobody was surprised to not see them. He bypassed the alarm systems at night and killed the family's dog if they had one. He would separate the family members under death threats and keep them apart for days. During those days, he would wear an outfit belonging to the father to assume the role as head of the household, as well as gloves to avoid leaving behind fingerprints. He would also terrorize the family members and make the children draw paintings (a technique used by family therapists to assess the family's situation).
On the last day of the family's captivity (which was always three), he would take them to the house basement and kill them by stabbing to death the children and wife (starting with the youngest child) before subduing the father and then staging his suicide by gunshot. Prior to doing so, he would bring them together for one final dinner. After killing them, he would take the fathers' wedding rings as trophies, keeping them in a jewelry box in a secret compartment in his office. It was revealed in his last appearance that he also physically abused the children and engaged in sexual acts with the girls as a reference to the physical and sexual abuse he suffered from as a child by his father, even though that wasn't said in his debut. It is likely that when he did sexually abuse the girls, he would wear a condom or use an object of some kind.
Arnold seems to have been inspired by Anatoly Onoprienko - Both were prolific serial killers and family annihilators who targeted families, broke into their homes to kill them, killed by various means, and had some twisted concept of mercy in their killings (Arnold viewed the families he slaughtered as dysfunctional, while Onoprienko killed the children of the families so they wouldn't become orphans).
He also seems to have been inspired by Yang Xinhai - Both were prolific serial killers and family annihilators with some sexual element in their crimes (Arnold would molest the children of the families he slaughtered while Xinhai would rape the women of the families), and were triggered by the rejection of a woman (Arnold's wife left him while Xinhai's girlfriend left him).
- Season One
- Season Five
- Season Six
- "Safe Haven" (mentioned)
- ↑ Karl was in possession of eight rings, five of which having definitely belonged to the named families he killed. However, it has been highly debatable as to whether the remaining three rings were taken from single victims (the fathers of families) or from families like his known victims, as it has been stated in "Outfoxed" that serial family annihilators start with single victims before moving on to entire families.