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It is important to realise that forensic science begins at the scene. Whoever is responsible for processing the scene, be it a civilian examiner or police investigator, needs to be able to recognise important physical evidence at the scene and preserve it correctly as no amount of high tech instrumentation or expertise will recover a botched crime scene investigation.

Not all scenes will be the same however certain practices need to be followed to successfully process a crime scene.

Securing the crime scene

It is the duty of the first police officer on the scene to take any steps necessary to make certain that the scene is kept as undisturbed as possible. If there too much movement at the scene by too many people, vital evidence is likely to be moved or destroyed.  Securing a scene can be very complicated say in the case of a fire or a road accident as the preservation of life will take precedence over anything else.

Recording the crime scene

Police officers and crime scene examiners will have limited time to investigate a scene, it is important therefore to record the scene, normally through still photography and videotaping by specialist photographers. Sketch diagrams and contemporaneous notes by attending police officers will also be important in recording the scene.

Systematic screening of the scene for evidence

Searching the crime scene is obviously important, how it is carried out depends on the scene. It may be as small and contained as a single room or it may be as large as a forest. It may include the dead (or living) body of the victim. Whatever the scene the search has to be as systematic and thorough as possible. Training is important, but so also is experience as it is often the experience eye which will pick up something that does not seem "quite right".

Collection and submission of physical evidence to the crime lab

While some of the evidence can be processed in situ, for example fingerprints, many items of physical evidence will need to sent to the crime laboratory for examination. The items need to packaged and marked clearly before sending to the lab to ensure correct identification of the physical evidence.

It is essential that any items of physical evidence can be traced from the crime scene to the laboratory to the lab report to the courtroom. This known as maintaining the chain of custody or continuity of evidence. If the chain is broken, the forensic investigation may be fatally compromised.

Safety at the crime scene

Quite often forensic scientists will attend a crime scene, not only in an investigative role but also in a occupational health and safety role. Fore example if a clandestine drugs lab is to be raided a forensic chemist will be on hand to ensure the many dangerous chemicals at such a lab can be secured safely.

For more information on crime scene processing and crime scene reconstruction the following web pages are of interest;

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