If you specifically meant Season 7, Episode 3, the "piece" of evidence crucial to that case involves:
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) [S7E3] The Fisher King
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 " If you specifically meant Season 7, Episode 3,
In this storyline, the Fisher King lures the team into a "quest" for the Holy Grail by sending them individual clues or physical items. Each team member receives a personal item or
Each team member receives a personal item or message while on vacation that leads them back to Virginia.
A man suffering from Capgras Syndrome (believing his loved ones have been replaced by imposters) after a traumatic brain injury.
In the context of the popular crime drama Criminal Minds , the "piece" usually refers to the physical puzzle pieces sent by the unsub Randall Garner—the Fisher King—to the BAU team.