Doubt

After being left grief-stricken by the death of his girfriend, Sarah Jacobs at the hands of his sworn enemy, Frank, Gideon, seeking peace of mind retreats to a winter cabin and begins writing a letter to someone while flashbacks show the team investigating a serial killer who is targeting brunette women at a small college in Flagstaff, Arizona. The BAU shuts down the campus, creates a detailed profile of the unsub, and arrests a suspect. However, the team members begin to have doubts about themselves when another woman is killed while the suspect is in custody which raises the possibility of a copycat being around the college campus. The episode ends with both UnSubs dying, Hotch getting a two-week suspension for his actions from Erin Strauss and Gideon's unseen departure from the BAU for good, leaving the team in shambles.