"I've been watching you all along, from the very beginning when you pulled into the Desert Bloom Inn. You set the wheels in motion the second you murdered Theo."
Crossford was one of over fifty illegitimate children of the leader of the Heaven's Mission, a cult based in a compound in southern Utah. The leader, who held extremist anti-government views, was said to have physically and sexually abused members, but a six-month investigation by Social Services turned up nothing. When he was ten, Crossford and his mother left the cult compound and moved to Phoenix, Arizona, where he spent his teenage years racking up a juvenile record. Probation officers found him to be cold, intelligent, and extremely manipulative, to the point of being psychopathic. When he turned sixteen, Crossford rejoined the cult and adopted his father's extremist views as his own. He also met one of his half-brothers, Theo Martin, and they became partners-in-crime. The two later broke off from the cult and moved to an apartment in Los Angeles, California, in 2007. Together, they began planning a terrorist attack against the U.S. government.
However, three months prior to "The Witness", Theo (who by that point had changed his surname to Koutranis) backed out of the plan when he fell in love with a woman, Tracy Senarak, with whom he had a brief romantic relationship with despite her current marriage. Crossford tried to reel Koutranis back in, to no avail, and proceeded to develop the plan without him. He purchased live samples of sarin from a disgraced chemist named Johann Geitman, who he then killed, and installed them into fish-feeding devices that would release the gas into the air once triggered. Six weeks prior to "The Witness", he installed one such device on City Link Bus 290, the bus Tracy frequently rode on, in hopes of killing her as retribution for stealing his partner. He then began following Koutranis around. One night, Crossford witnessed Koutranis being killed by Tracy's husband Charlie, who intercepted Koutranis's attempt at meeting up with Tracy again. Realizing he had a potential patsy, Crossford began stalking Charlie, intending to blackmail him and use him to help stage attacks.
After six weeks, the sarin Crossford installed on City Link Bus 290 was released into the air, killing the driver and eight passengers. After the bus nearly crashes at a bus stop, a man climbs aboard to investigate and is killed by the sarin as well. As the attack catches national headlines, Crossford sends Charlie a threatening email claiming that he knew what he did. When Charlie responds with a demand to know who was contacting him, he calls himself "a witness" and tells him to do something for him or else he will call the police. Charlie refuses just as he receives a package. Later, the package turns out to contain a cellphone that Crossford uses to communicate with Charlie when he answers his call. He threatens his daughter Jolene, reminding him of what will happen if he goes to jail. After this and a visit from the BAU, Charlie agrees to the terms, breaking into Geitman's home and stealing his laptop. In the process, he discovers Geitman's body and nearly gets found by the police, who were tipped off by Crossford.
Crossford then calls Charlie the next morning to pick up the laptop, claiming he didn't know about the body. When Charlie claims that he is tied to a murder now, Crossford laughs and reminds him of how he killed Koutranis. He then tells Charlie to drive to a warehouse and pick up a package, continuing to use Jolene as leverage. To further intimidate him, he shows up at Charlie's office under the pretense of asking his wife about his half-brother's whereabouts. As Charlie receives the package, Crossford places more fish-feeding devices full of sarin inside the trunk of the former's car. Realizing he is going to be set up for another attack, Crossford calls him once more, but Charlie threatens that he will turn in the phone to the FBI. Crossford tries to calm him down, but then threatens him by claiming to have Jolene. He goads Charlie into chasing him by car into the local federal building using a mannequin dressed in copies of Jolene's clothes. He abandons the truck and reaches the best vantage point to see the results of the second attack. However, the BAU, having already deduced his plan and sealed the parking garage, promptly arrest him.
Crossford first killed Johann Geitman by shooting him once in the head, likely with a handgun. Then, he placed small amounts of sarin into the slots of fish-feeding devices, which would release the gas into the air in an aerosolized form once triggered. During the city bus attack, Crossford placed only one feeding device inside the bus and waited six weeks (the amount of time it took for the devices to activate). During the attempted attack on the federal building, he placed dozens of feeding devices in the trunk of Charlie's car, lured him into a parking garage where many employees would gather (and where the ventilation systems to the entire building were located), and waited for the devices to activate.
The recent sarin gas attack is most likely the work of only one or two homegrown terrorists, although they may have spun off from a larger group. Their rationale may be ideological or revenge-based, but it is possible that they are only using ideology as a cover. The fact that the unsub(s) chose sarin as their weapon and is/are using a time-release device means that he/they is/are criminally sophisticated, meticulous, and extremely patient. At least one of the unsubs may be older, aged in his late 30s or 40s. The contained nature of the attack indicates that the partnership between the two conspirators has fallen apart and only part of the plan was carried out. Given that the sarin was from an old stockpile, the bus attack was simply a test of its potency. Therefore, something much larger in scale is being planned, and the longer the unsub is free, the more confident and brazen he will become. It is possible his next target will be another mode of public transportation; or an airport, a train terminal, or a bus terminal.
Crossford has some similarities to Timothy McVeigh and may have been based on him. Both were homegrown terrorists who had extreme anti-government views, had accomplices who assisted them in the acquisition of their weapons (Mitchell was given the sarin gas by Johann Geitman; McVeigh had Terry Nichols's help in constructing the fertilizer bomb), and were spurred to commit attacks against the U.S. government following the federal dismantling of notable religious cults, including the Waco siege. They also sought to attack a federal building with the aim to kill as many employees as possible (although McVeigh was successful in his attack whereas Crossford's was foiled). The backstory of Crossford and Koutranis, and their initial plan to work together in committing terrorist attacks, may have also taken some inspiration from Tamerlan and Dzhokhar Tsarnaev, the Boston Marathon bombers.
Crossford also has some elements in common with a poison gas plot in Tyler, Texas. Like the plotters William Krar, Judith Bruey, and Edward Feltus, Crossford was a member of an anti-government group who concocted a scheme to attack the U.S. government using chemical weapons. However, unlike the plotters, Crossford was successful in enacting his plan.
- July-October 5: Theo Koutranis (his half-brother; stalked only)
- October 5: Johann Geitman (the sarin supplier; shot in the head, presumably with a handgun)
- October 6: Ten killed in the City Link Bus 290 sarin gas attack:
- The unnamed driver
- Michael Hoffman
- Louis Rostro
- Six other unnamed passengers
- Unnamed man (climbed aboard the bus while investigating and had a fatal exposure to the sarin)
- Tracy Senarak (target victim; intended to kill; wasn't aboard the bus at the time of the attack)
- October 7: The attempted sarin gas attack on the federal building:
- Note: Considering he intended to leave Charlie as a patsy for the federal building attack and escape with vials of sarin, Crossford was likely planning another attack against the U.S. government, though no potential targets were specified.
- Crossford is similar to Season Four criminal Chad Brown. Both were homegrown terrorists who used poisons in their attacks (Crossford used sarin; Chad used modified anthrax), killed the people who supplied them with their poisons, were based on real-life terrorist cases (Crossford is similar to Timothy McVeigh; Chad is similar to the Amerithrax case), and were arrested while they were attempting to commit another attack.
- Crossford's scheme is extremely similar to the final act of the 1999 mystery thriller film Arlington Road. Both scenarios involved a homegrown terrorist attack on an FBI building using a patsy carrying a weapon (which was capable of affecting a large area) in the trunk of his car, with the patsy being tricked into going into the building's garage parking lot by making them believe their own child was abducted and is being driven to the location in a van.