Very little is known about Colfax, other than she became an FBI agent. By the events of "The Witness", she was working in a high position in the FBI's Los Angeles field office. She has commonly assisted the BAU during cases in Los Angeles.
When a city bus is attacked with sarin gas, Colfax summons the BAU to assist the federal investigation. She points the team to security footage of a man named Charlie Senarak, who boarded the targeted bus before the attack occurred. He then stepped off it soon after to clean his hands and feet with drinking water, but apparently missed it as it left. Colfax then identifies him and where his workplace is. She is later present when the BAU gives their profile of the unsubs, who they assume is a two-person team. Later on, she and the BAU exonerate Charlie for involvement in the attack, but suspect him in what appears to be an unrelated murder. Meanwhile, the real unsub tricks Charlie into breaching the Los Angeles field office with a car full of sarin vials. Colfax assists in the evacuation of the building.
Colfax summons the BAU back to Los Angeles when two women are murdered by a spree killer. When the team arrives at the field office, she informs them of a third murder and tells them the list of suspects that they interrogated, clarifying that none of them were involved. Afterwards, Colfax receives a text on her phone that security footage of Patricia Brannon's apartment complex is up. She and the rest of the team look through the footage to see how the unsub is entering the victims' homes. It is at that point they realize that the unsub is an FBI agent or is posing as one. Later, Colfax and the other police officers are given the unsub's profile. The following night, Colfax lures the unsub into a trap to apprehend him by using the communicator. Afterwards, Colfax, along with Rossi and Morgan, are informed by Garcia about a retired FBI agent named Ed Sulzbach and are given his address.