Jason Gideon is called back from a six-month leave from the Behavioral Analysis Unit to profile a killer. Meanwhile, the team flies across the country to Seattle when another young woman goes missing at the hands of another killer.
- Leanne Adachi - College Student #1
- Kirsten Adler - Brick Agent
- Kwesi Ameyaw - Police Officer #1
- Trevor Beeby - SWAT Agent
- Artine Brown - Detective Holmes
- Louise Grant - Mrs. Slessman
- G. Michael Gray - Imaginary Unsub
- Lukas Haas - The Footpath Killer
- Jeff Hephner - Boy in Image
- Chelah Horsdal - Heather Woodland
- Andrew Jackson - Officer Timothy Vogel
- Hiro Kanagawa - Seattle ASAC
- David Lewis - David Woodland
- Natalina Maggio - College Student #2
- Jamie Mayo - Sister
- Meredith Monroe - Haley Hotchner
- Alonso Oyarzun - FBI Student
- David Pearl - Police Officer #2
- DJ Qualls - Richard Slessman
- Malcolm Stewart - Warden
- Joanne Whalley - Karen Donovan
- George Metesky, The Mad Bomber
- John Allen Muhammad and Lee Boyd Malvo, The DC Snipers
- Theodore Kaczynski, The Unabomber
- Ted Bundy
- The Lipstick Killer
- David Berkowitz, Son of Sam
- Lawrence Bittaker and Roy Norris, The Toolbox Killers
- Charles Manson
- Henry Lee Lucas, The Confession Killer
- Jeffrey Dahmer, The Milwaukee Cannibal
- "Penitentiary" by Citizen Cope
- "In The Air Tonight" by GodHeadSilo
- "Enter Sandman" by Metallica
- "Hold Back" by The Living Sisters
- "Rock Music" by The Pixies
- Jason Gideon: Joseph Conrad said, "The belief in a supernatural source of evil is not necessary. Men alone are quite capable of every wickedness."
- Jason Gideon: Emerson said, "All is riddle, and the key to a riddle is another riddle."
- Jason Gideon: Winston Churchill said, "The farther backward you can look, the farther forward you will see."
- Jason Gideon: Nietzsche once said, "When you look long into an abyss, the abyss looks into you."
- "Extreme Aggressor" is a term referring to a strategy type for Go, a heavily strategic yet relatively simple Chinese board game that was played by Richard Slessman. This strategy was pointed out by Reid as an extremely difficult type of strategy due to its rather aggressive nature.
- The episode marks the most times a different bookend quote was recited in a single episode, with a total of four, all recited by Gideon.
- The Metallica CD found in the laptop of Richard Slessman is the soundtrack to Some Kind Of Monster, which does not include "Enter Sandman", the song that allowed Reid to solve the laptop's password.