|Name||Karl Arnold, Sr.|
|Family|| Unnamed father (mentioned; status unknown)|
Fay Arnold (ex-wife)
Karl Arnold, Jr. (son)
Sarah Arnold (daughter)
|Pathology|| Serial Killer|
|Modus Operandi|| Stabbing (mothers and children)|
|No. of Victims|| 8+ killed|
|Portrayed By||Neal Jones|
|First Appearance||"The Fox"|
"Wives wither... children perish... but me? I'm an excellent father."
Karl worked as a family psychiatrist. It was revealed in "Outfoxed" that he was abused (and possibly molested) by his father and, over time, 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.
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 Dunkens's house, where he used the Dunkens 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 that?"
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 is active in Hampton, Virginia. Hotch and Prentiss interview Karl at 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, which she is later of herself by for "flirting" with Karl to get info. At the end of the episode, Karl reveals that one of them also contained a newspaper article about George Foyet's attack on Hotch, signed with his signature Eye of Providence, as a way to announce that he was returning. As Hotch left, Karl laughed in delight at his despair.
Organized killers are typically skilled workers with above-average intelligence, a high birth status, and are often male. This unsub is both socially and sexually confident. He also does extensive research about his victims, keeping all of the acquired information in a book or journal to ensure that nothing is left to chance, and takes a lot of time to make up a good plan before killing them. When asked why Karl killed the way he did, he replied that it was "to show what happens when the head of household isn't strong". He is also obsessive-compulsively neat, as revealed by his well-organized office and his hatred of things that are out of place, such as when he notices the misplaced Miller and Crawford crime scene photos, something that can be considered by many to be trivial. According to Prentiss in "Outfoxed", Karl was sexually motivated and killed the 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."
Karl murdered 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 was seeing another therapist). 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 alarms 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, until he took them to the house basement and killed them by stabbing to death the children and wife (starting with the youngest) before subduing the father and then staging his suicide by gunshot. During those days, he would terrorize them, make the children draw paintings (a technique used by family therapists to assess the family's situation). On the final day, he would bring them together for one final dinner. After killing them, he would take the wedding rings as trophies. It was revealed in "Outfoxed" that he also physically abused the children and engaged in sexual acts with the girls, even though that wasn't said in "The Fox".
- Unspecified dates:
- Three unnamed men or families killed prior to The Fox
- The Kegan family
- The Ness family
- The Linford family
- October: The Miller family
- The unnamed stepfather
- Reese Miller (mother)
- Ty Miller (son)
- Reese's unnamed daughter
- November 4: The Crawford family
- Christopher Crawford (father)
- Allison Crawford (mother)
- Sam Crawford (son)
- Emily Crawford (daughter)
- November 9: The standoff at the Dunken home:
- The Dunken family (intended)
- Harry Dunken (father)
- Robin Dunken (mother)
- Jackie Dunken (daughter)
- The unnamed baby son (briefly held hostage, then thrown violently at Gideon, but he was safely caught)
- Derek Morgan (attempted; tried to stab him)
- The Dunken family (intended)
- October: The Miller family
- ↑ Karl was in possession of eight rings, five of which having definitely been from 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.