|“||You better not give me any trouble.||”|
— Allen to Billy Henderson
Nothing is revealed about Allen's early life, not even his full name. In 1975, he became a real-estate developer and founded a construction company in the small town of Crawford, a business that prospered over the years. Among his clients were the local police department, who hired him to build for them on multiple occasions, including their station. The same year, he also married a woman with whom he had a daughter, Samantha, two years afterward. When Samantha was five years old, her mother passed away from cancer. Growing up, she spent most of her time playing sports since Allen was often busy at work. Underneath his façade, Allen was also a serial killer and pedophile who abducted and killed young boys, using construction sites belonging to his company to lure them. He would dispose of their bodies at his first development site in Mesa, adding house after house to it in order to bury the boys' bodies underneath them. He would also take any toys or other possessions that were with the victims and give them to Samantha as gifts. Sometime during 1982, before her mother died, Samantha had witnessed Allen holding a boy captive but refused to accept that her father was capable of such actions and repressed those memories. Allen's motivations for his crimes presently remain unknown. In 2004, Allen abducted a boy named Angel Suarez, holding him captive and raping and torturing him for eight years until 2012, when Angel escaped while being transported by Allen, eventually being found by the Nelsons, a family traveling in their car. Allen immediately abducted another boy named Billy Henderson, leading to the BAU being called in.
For the first act of episode, Allen is mostly seen checking on Billy Henderson in his underground cell. He is fully seen for the first time when Samantha comes to visit him, asking to search the basement for her catcher's mitt and stating that she plans to coach softball with it. At first, Allen is reluctant, telling her that there are many boxes down there, but then allows her to go look inside. Samantha searches around, but Allen quickly finds the baseball mitt and gives it to her; she then leaves the house. Little does he know that Samantha was actually wired by the BAU, who suspect Allen of being the unsub, with her being instructed by Prentiss to search the basement, where it is assumed Allen is keeping Billy Henderson. Feeling that the authorities are closing in on him, Allen decides to take Billy to the development site of Mesa. However, the BAU have already identified Allen as the unsub and follow him into the desert, where they find him burying Billy. Allen flees and is pursued by Morgan, who tackles him to the ground and starts punching him, angered by what he did to Angel, whom he befriended. However, he is stopped by Rossi before he can beat Allen to death. Meanwhile, Hotch successfully digs Billy out. Allen is last seen taken into custody, where he is met by a shocked Samantha.
Allen targeted young boys, using his construction sites to attract their attention. He would give them rides in a construction vehicle. He may have lured some of his victims under the ruse of being trouble or needing assistance as hinted during a conversation. He is also extremely confident. After abducting them, he would hold them captive in a secret compartment under the floor of one of the basements in his property. Over the course of several years, he would rape and torture them as well as bite them. After some time, likely when they became too old for him, Allen would murder them through unspecified means and dispose of their bodies at his first development site, burying them at the foundation of the next house that was to be built. Since he tried to kill Billy Henderson by burying him alive, it is possible that he did the same to his other victims. He would also, take toys and other possessions they had on them as trophies and give them to Samantha as gifts.
The unsub is a pedophilic male who is smart enough to cover his tracks when he abducted Billy Henderson. He is too controlled to allow his victims to escape and may have tried to move Angel to another location, which is how the latter was able to escape. He has a psychiatric disorder that drives everything he does, and he will do whatever it takes to hide Billy. However, he will willingly also sacrifice him if that means protecting his own freedom. Everything that this unsub, does is methodical; he had a secure place to keep Angel for years, but when Angel escaped, he did not mourn the loss and drove straight over to Flagstaff instead. It is believed that the unsub specifically targeted Billy and may have also singled Angel out as well. This unsub knows his victims and may be a friend, neighbor, coach, or a parent. He will have a secondary location to keep his victims and it will be close to his home. He would only get rid of a victim if he had another boy waiting for him to abduct, meaning that he has met his victims before. He keeps his victims for years and the disposal sites would be someplace special, giving him a reason to revisit them; it is most likely a location having to do with his work.
Allen has some similarities to John Wayne Gacy - Both were overweight serial killers and serial rapists who were married and had a daughter, lost their wives prior to their killings (though Allen's died while Gacy's divorced him), owned construction companies, targeted young males, lured their victims with ruses, would torture them in various ways, and buried their bodies in secret compartments after killing them.
Allen is also similar to Edward Edwards - Both were overweight serial killers and rapist with daughters responsible for turning them in off repressed memories of the crimes both killers are guilty of.
Note: The years denote when the known victims were abducted. The only exception to that is the unnamed 1982 victim
- Presumably killed numerous unnamed victims over the course of at least 30 years prior to Foundation
- Unspecified date and location in 1982: Unnamed victim
- Unspecified date in 2004, Crawford, Arizona: Angel Suarez (abducted, held captive, raped, and tortured; he escaped on March 30, 2012)
- March 30, 2012, Flagstaff, Arizona: Billy Henderson (abducted, raped and attempted to bury alive; was rescued the next day)
- Garrett M. Brown, the actor who plays Allen, previously portrayed a serial killer on Law & Order: Special Victims Unit.
- It is actually unconfirmed whether he is a serial killer or not because only one victim was confirmed in the episode, however Allen is listed as such because of the fact that he was active for at least 30 years and his experience in abducting his victims, holding them captive, and then killing them. There was also a scene that showed many houses he built at his first development site as he tried to kill Billy Henderson, implying many more victims.
- Same as above.