Wives wither... children perish... but me? I'm an excellent father.
Arnold during his interrogation with Morgan

Karl Arnold, Sr., a.k.a. "The Fox", is a prolific serial killer, family annihilator, and pedophile who first appeared in Season One of Criminal Minds.


Karl worked as a family psychiatrist. It was revealed in "Outfoxed" that he was physically abused and molested by his father. Over time, he developed an intense self-hatred. At some point in his life, he married a woman named Fay, with whom he had two children, Karl Jr. and Sarah. He was very controlling, bordering on obsessive-compulsive, which resulted in a divorce about five years prior to "The Fox" in which Fay won full custody of their children. After that, Karl took some time off from his job, became unfocused, and started drinking heavily. Prior to "The Fox", he infiltrated the homes of families he was treating, took them hostage, and pretended to be their father before killing them.

The Fox

After Karl kills 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. Karl 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 Karl 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 Karl, 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 "Outfoxed", a spree killer targeting entire families becomes active in Hampton, Virginia. Hotch and Prentiss interview Karl 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 Karl to get info. Despite Prentiss discovering that the unsub is a female, Karl continues to refer to his admirer as "he", and when Hotch tells him that he is done with him, Karl reveals the admirer said the same thing. Hotch then takes the journal where Karl 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 Karl, a fact Karl was aware of, and that Foyet was using him to get a message to Hotch. As Hotch left, Karl laughed in delight at his despair.

Arnold s5

Karl in prison, assisting Hotch and Prentiss in "Outfoxed".

A year later, while investigating another spree killer specifically targeting families, Prentiss brings up Karl as an example of a family annihilator.


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 "Outfoxed", Karl 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.

Modus Operandi

"...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."

Karl 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 "Outfoxed" 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 "The Fox". It is likely that when he did sexually abuse the girls, he would wear a condom or use an object of some kind.

Real-Life Comparison

Karl has some similarities with Yang Xinhai, a.k.a. "The Monster Killer", a prolific serial killer and family annihilator. Like Xinhai, he would break into their victims' homes at night and kill them, sexually assaulted some of their female victims, and were triggered by the rejection of a woman (Arnold's wife divorced him; Xinhai's girlfriend allegedly broke up with him).

He is also similar to the Ukrainian serial killer Anatoly Onoprienko, a.k.a. "The Beast of Ukraine" or "The Terminator", one of the most prolific serial killer and family annihilator in Ukraine. Both would break into homes and kill the whole family at night. The difference is he didn't stalk his victims, Anatoly just saw a house and killed everyone with a gun.

Known Victims

  • Unspecified dates and locations from 2000(?) to 2005:
    • Three unnamed men or families[1] killed prior to The Fox
    • The Kegan family
      • At least one unnamed parent
      • At least one unnamed child
    • The Ness family
      • At least one unnamed parent
      • At least one unnamed child
    • The Linford family
      • At least one unnamed parent
      • At least one unnamed child
  • 2005:
    • October, unspecified location in Maryland: The Miller family (held hostage for three days before being killed)
      • The unnamed stepfather (also stole his wedding ring and framed him for the murders of his family)
      • Reese Miller (mother)
      • Ty Miller (son; also physically abused before being killed)
      • Reese's unnamed daughter (also physically abused and molested before being killed)
    • November 1, Arlington, Virginia: The Crawford family (held hostage on October 29 before being killed three days later)
      • Christopher Crawford (father; also stole his wedding ring and framed him for the murders of his family)
      • Allison Crawford (mother)
      • Sam Crawford (son; also physically abused before being killed)
      • Emily Crawford (daughter; also physically abused and molested before being killed)
    • November 8, unspecified location in Virginia: The Dunken family (held hostage and intended to kill; all were rescued the next day)
      • Harry Dunken (father)
      • Robin Dunken (mother)
      • Jackie Dunken (daughter; presumably physically abused and molested)
      • The unnamed baby son (briefly held hostage, then thrown violently at Gideon, but he was safely caught)
    • November 9, unspecified location in Virginia: Derek Morgan (attempted; tried to stab him)



  1. 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.