Real-life (twin) brother and sister David Tom and Nicholle Tom play siblings Georgie and Connie Galen.
In the scene where Rossi and Prentiss are speaking to the carnival worker about his son, the clown/unsub, "(LE)GACY" can be seen on a building in the background. John Wayne Gacy was a serial killer who became known as the "Killer Clown" due to the clown costume he often wore to entertain children at neighborhood parties.
The end quote is "There is no formula for success, except perhaps an unconditional acceptance of life and what it brings." by pianist Artur Rubinstein. Previously, in P911 (2006), John Rubinstein, Artur's son, had a guest appearance as a suspect.
Dennis Christopher (assistant warden), also played a serial killer on Profiler (1996), a show similar to Criminal Minds. He was known as "Jack of All Trades" and was obsessed with the show's star, Samantha Waters. Criminal Minds bears a great many similarities to that show.
The truck that Connie sees in the parking lot at the strip club is a Ford F-250 diesel.