The characters Richard Haywood and Justin Pendleton are loosely based on real-life murderers, Richard Loeb and Nathan Leopold.
The old lodge on the bluff was constructed especially for the movie and was torn down after filming was completed. The interior scenes were shot on a set.
Richard's car, a Mustang, is the same type of car driven by Steve McQueen in Bullitt (1968). Ryan Gosling suggested that the car be used, as he is a fan of McQueen.
The scene near the end of the movie, where Ryan Gosling licks Sandra Bullock's face, was not scripted. After a few takes, Gosling asked Bullock if it would be okay if he added it in to prove his character's sick nature.
Todd Field's role as a murder suspect was deleted from the final print.
Ryan Gosling threw up as he filmed the murdering scenes.
The high school scenes were originally slated to be filmed at San Luis Obispo High School. The superintendent changed his mind before filming could take place due to the content of the script.
On the face of the clock seen in front of the police station, it says, "Spend Time With Those You Love".
The title refers to the song "Murder by Numbers," written by 'Sting' and Andy Summers and performed by The Police, about planning the perfect murder.