The role of Crime Scene Agent was originally written for Priscilla-Leah McCarthy but she was busy studying Forensic Science and recording her own music that fellow Beast star Mark Scullion stepped into the role.
The film was originally intended to open with a car chase, involving the Detectives and the Killer, that was filmed and edited and featured Mitchell Cartwright, but the directer felt the pace was set too high too early by the car chase and subsequently cut it from the film.
At different parts of the film stand-ins for the body of the Killer or Assassins are played by Mark Scullion, Liam O'Riordan and director Carl Thomason, whilst the photo of the suspected killer is that of Andy Blaxsell.
The bathroom scene where Detective Neeson is drinking and then briefly confronted by Random Officer 1 was filmed in the staff toilets of Sainsburys in Letchworth, UK.
In the late on scene in Captain Smith's office when Detective Neeson confronts the Captain, the book that sits on Captain Smith's desk is the screenplay of Stanley Kubrick's Eyes Wide Shut (with the short story 'Dream Story' by Arthur Schnitzler).