Karl Arnold

Karl Arnold was a serial killer who appeared in The Fox.

History
Karl worked as a family psychiatrist. At some point in his life, he married a woman named Faye with whom he had two children, Karl Jr. and Sarah. He was very controling, bordering on obsessive-compulsive, resulting in a divorce which ended with Faye getting 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 two families he was treating, the Millers and the Crawfords, and killed them. At this point, the BAU were called in to investigate. After tracking him down, they 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 the BAU searched his office, they found a box containing a number of wedding rings, implying that Karl has killed many more families before the Millers and the Crawfords without being detected.

Season Five
In the episode Outfoxed, a serial killer targeting entire families is active in Hampton, Virginia. Hotch and Prentiss interview him at Red Onion State Prison, where Karl assists in their investigation. At the end of the episode, Hotch is shocked to find that Karl has been in contact with George Foyet and that the fugitive killer plans to return.

Profile
Organised killers are typically skilled workers with above-average intelligence, a high birth status and are often male. He is both socially and sexually confident. He does extensive research about his victims and takes a lot of time to make up a good plan before killing them. He keeps all this information in a book or journal, ensuring that nothing's left to chance, and never leaves anything out of place. When asked why Karl killed the way he did, he replied "to show what happens when the head of household isn't strong". He also appeared to be obsessive-compulsively neat, as revealed by his well-organised office.

Modus Operandi
Karl would strike when 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 slashing the children and wife, starting with the youngest, brought down the father and staged 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.

Known Victims

 * The Miller Family (Reese, her new husband, their son Ty and their daughter)
 * The Crawford Family (Christopher, his wife Allison and their children Sam and Emily)
 * The Dunkens family (attempted, Harry, his wife Robin, their daughter Jackie and an unnamed baby boy)
 * At least six other families (a box holding eight wedding ring trophies, one Reese's husband's and another Chris Crawford's, is found in Karl's office)

Appearances

 * Season One
 * The Fox
 * Season Five
 * Outfoxed