A man suffering from Capgras Syndrome (believing his loved ones have been replaced by imposters) after a traumatic brain injury.
If you specifically meant Season 7, Episode 3, the "piece" of evidence crucial to that case involves: [S7E3] The Fisher King
In this storyline, the Fisher King lures the team into a "quest" for the Holy Grail by sending them individual clues or physical items. A man suffering from Capgras Syndrome (believing his
Spencer Reid is cast as "Sir Percival" and is given the task of asking the question that will "heal" the King. Context for S7E3: " Dorado Falls " Context for S7E3: " Dorado Falls " The
The team has to piece together his military background and the specific trigger of a car accident to stop his mass murder spree at an internet security company. "Criminal Minds" The Fisher King: Part 1 (TV Episode 2006)
The "piece" for the puzzle was a section of a large map or picture that, when assembled, revealed the location of his "Grail"—his daughter, Rebecca.