Reid mentions only three known instances where two different serial killers operated out of the same city at the same time. During 1977, both David Berkowitz (Son of Sam) and Paul Bateson were killing in New York City. In Phoenix, Arizona, in 2006, authorities were searching for both the Baseline Killer and a serial shooter. From 1991 to 1996, two different people were killing independently in New Orleans, leaving bodies in swamps. Police suspected that Russell Ellwood killed as many as 15 of the victims but believed that another killer was responsible for the others.
In the scenes with the children watching TV as their mother leaves, Austalian V8 Supercars are on the TV (from approximately 2002).
The real name of "The Hollow Man" is never revealed.
The Missouri Herald, the newspaper used as the St. Louis-area paper, closely resembles the St. Louis Post-Dispatch, the real newspaper for the city.