The character of Emily Prentiss was named for Special Agent Emily Vacher, the real-life agent who worked in the Cybercrimes Unit for the Albany division of the FBI.
Dayne Johnson, Department Head-Makeup Artist, makes an uncredited appearance in this episode as the person who applies make-up to the female police officer pretending to be dead as a lure to catch the unsub.
Reid: When Mill Creek kills, the Hollow Man shoots another prostitute.
Morgan: So, one doesn't want to be outdone by the other. Sounds like sibling rivalry to me.
Hotchner: They've been killing independently of each other for a year now.
Gideon: With each kill, they're learning something... from the other.
Jim Meyers: This is all just a guessing game, isn't it?
JJ: No, it's behavioral analysis.
Agent Sheridan: Sunny? Holden?
Hotchner: They're characters from Catcher in the Rye.
Reid: Widely accepted as a beloved book of sociopaths. Mark David Chapman quoted it after killing John Lennon.
Hotchner: Deranged minds identify with Holden's alienation and detachment.
Reid: We always say serial killers make the best profilers.
Hotchner: Yeah, but this guy's dead on.
The music featured in this episode was "Field Below" by Regina Spektor.
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