i) The Crime Scene Examiner within the Police Force.
The main function of a Crime Scene Examiner (also known as a Scenes of Crime Officer – SOCO or Crime Scene Investigator – CSI) is to record, gather and preserve all available potential physical evidence to support the investigating officer in their inquiry [Pep05]. Many police forces have a scientific support department that offers a range of forensic crime scene examination capabilities; however, the overall responsibility for an investigation is that of a police officer [Elm10]. Where an officer feels that a particular aspect of forensic examination could be beneficial to the investigation, they would make a request to a CSI. In order to maximize the potential forensic recovery, officers give a full and comprehensive account of the incident, outlining the points to prove to the CSI[Tru09]. An overall department head, scientific support manager or equivalent, has the overall responsibility for the scientific support department, which will generally contain a CSI Unit, a Fingerprint Bureau, a photographic/video unit and a chemical development laboratory [Bea09]. .
ii) Locard's Principle of Exchange.
The basic principle of forensic science is "every contact leaves a trace", the phrase being both well-known and universally accepted in the forensic community[Ran10]. In 1920 Dr. Edmund Locard published his principle suggesting that when one object comes into contact with another, something is exchanged between and taken away by both objects[Pep05]. This means that any physical contact between individuals, or between an individual and a place or object invariably results in the transference of traces of physical evidence[Jac08]. One example demonstrating this principle is the case of Sarah Payne, linking her to her killer, Roy Whiting. Investigators found on Sarah's shoe fibres from the perpetrator's clothes as well as from an unusual curtain found in his van; furthermore, a hair was found on a sweatshirt seized from Roy that was later compared to Sarah's DNA[The01].
