BIOLOGICAL MATERIAL – COLLECTION

10 Apr

BIOLOGICAL MATERIAL – COLLECTION, CHARACTERIZATION AND STORAGE

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. Thesuccessinfindingbiologicalmaterialdependsuponthesearchmethodemployed 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. Evidence collection The methods used for collection will vary depending on the type of sample. Dry stains and contact marks on large immovable items are normally collected using a sterile swab that has been moistened with distilled water [9, 10]; in other cases, scraping or cutting of material may be more appropriate. Lifting from the surface using high quality adhesive tape is an alternative method for collecting epithelial cells [11]. Liquid blood can be collected using a syringe or pipette and transferred to a clean sterile storage tube that contains anticoagulant (EDTA), or by using a swab or piece of fabric to soak up the stain, which should be air dried to prevent the build up of microbial activity [4]. Liquid blood can also be applied to FTA® paper that is impregnated with chemicals to prevent the action of microbial agents and stabilize the DNA. Smaller moveable objects, such as weapons, which might contain biological material are packaged at the scene of crime and examined in the controlled environment of the forensic laboratory. The same range of swabbing, scraping and lifting techniques as

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