Garcia reports that one of the murderers is from Derry, Maine, which is the fictional town created by Stephen King, that serves as the setting for many of his novels, most famously his 1986 book, 'It'.
The sketches the victims used to describe "the monster" were drawn by Matthew Gray Gubler. To make them appear different, he drew one with his right hand and the other with his left hand.
The names Karras, Merrin and McNeil are all names of characters in The Exorcist.
Jennifer Love Hewitt's character Kate mentions that she was afraid of a girl called Melissa Gordoner when she was young, which is very similar to the name of her Ghost Whisperer (2005) character of Melinda Gordon.