Identification and characterization of biological evidence

Searching for biological material, both at the crime scene and in the forensic laboratory is performed primarily by eye. In the laboratory, low power search microscopes may help to localize stains and contact marks. Alternative light sources have been found to assist with finding biological material both in the field and in the laboratory. Epithelial cells, saliva and semen stains may fluoresce at different wavelengths of light compared with the background substrate and therefore may become visible [6-8]. A range of light sources is available and these can either operate at fixed wavelengths or a variable number of wavelengths that are suitable for detecting different types of stain.

Searching a crime scene or items recovered from a crime scene for blood can be aided by the use of luminol (3-aminophthalhydrazide). This chemical can be sprayed onto a wide area and will become oxidized and luminescent in the presence of haemoglobin, which is found in red blood cells. It is necessary to be able to darken the area that is being searched in order that the luminescence can be detected. Luminol can also be used

What Scene Crime Officers Wear

Figure 3.3 It is standard practice for scene of crime officers to wear full overalls, shoe covers, gloves and face masks when collection biological evidence from a scene of crime. Even with these precautions it is possible for crimes to be contaminated by forensic investigators and it is becoming common for the DNA profiles of police officers and scene of crime officers to be stored on a database; any profiles recovered from the scene of crime can be checked against this elimination database to rule out the possibility of a profile coming from an investigating police or scene of crime officer

Figure 3.3 It is standard practice for scene of crime officers to wear full overalls, shoe covers, gloves and face masks when collection biological evidence from a scene of crime. Even with these precautions it is possible for crimes to be contaminated by forensic investigators and it is becoming common for the DNA profiles of police officers and scene of crime officers to be stored on a database; any profiles recovered from the scene of crime can be checked against this elimination database to rule out the possibility of a profile coming from an investigating police or scene of crime officer in the more controlled environment of the forensic laboratory and can be particularly useful when searching clothing for trace amounts of blood.

The success in finding biological material depends upon the search method employed and also on the integrity and state of the scene. In the UK, biological material is found at approximately 12 % of investigated crime scenes, this figure can go up significantly if the crime scene is exhaustively searched.

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    What do Scene of crime officers wear?
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