[s7e3] The Fisher King -

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)

However, the episode titled is actually the two-part finale of Season 1 (Episode 22) and the premiere of Season 2 (Episode 1). If you are looking for Season 7, Episode 3 , that episode is titled " Dorado Falls " . The Puzzle Pieces in " The Fisher King " (S1E22 / S2E1) [S7E3] The Fisher King

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.

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. If you specifically meant Season 7, Episode 3,

Each team member receives a personal item or message while on vacation that leads them back to Virginia.

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 " The Puzzle Pieces in " The Fisher King

A man suffering from Capgras Syndrome (believing his loved ones have been replaced by imposters) after a traumatic brain injury.