Mitchell Crossford was the main antagonist of the Criminal Minds episode 'The Witness'.
Crossford was one of over 50 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.
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 was 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 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.