The X-Files 9x17

When an FBI cadet with amazing profiling skills approaches Doggett, Reyes, and Scully with a lead on a suspect in a series of recent murders, he claims the same killer is responsible for the death of Doggett's son. The agents find themselves wondering if his knowledge of the deaths is because of his obsession with the cases he has studied at Quantico, or if he is in some way involved in the murders.