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Trace evidence

Trace Evidence is the term given to the range of  specialist analytical services undertaken by the Key Forensic chemistry department.

A window may often be broken at the point of entry in a burglary, or as a result of criminal damage. Similarly, glass objects may be broken during an assault. If someone is close to breaking glass then tiny fragments of glass are transferred onto their skin, hair and clothing. These glass fragments can be recovered at the forensic laboratory and compared by our glass experts using physical and chemical tests to the control glass from the crime scene through our trace evidence investigations. If the recovered glass fragments match the control glass, then the forensic examiner will decide on the strength of evidence based upon the number of matching fragments and the frequency of occurrence of the control glass.

Paint and Particulates

Minute fragments of paint, plastic or other materials may be recovered from the clothing or tools of someone who has forced entry into a building or vehicle.

With our trace evidence investigation service, the layer sequence of fragments of recovered paint can be determined by microscopy and compared to that of the control paint from the scene. In addition, the physical and chemical properties of the paint or other particulates can be measured and compared to the control materials from the scene.

The significance of the evidence will depend to a large extent on how unusual the material is that has been transferred to the suspect during the incident.

Also falling within Particulates evidence is the Gunshot Residue (GSR) or Firearms Discharge Residue (FDR) evidence type. GSR is the collective term for microscopic particles which are emitted from a firearm when it is used. GSR may contain Microscopic metallic particles formed when the shock sensitive chemicals in the primer charge are ignited by the firing pin. Particles of un-burnt propellant which could contain detectable additives. Microscopic metallic particles originating from the projectile, the cartridge case or the firearm. GSR can be acquired by Discharging a firearm. Being close to a discharging firearm (the GSR cloud can travel up to approximately three metres forward from the point of discharge and less to the sides). Direct contact with a recently discharged firearm or a discharged cartridge case. Contact with a surface or object bearing GSR. Contact with a person bearing GSR (including Armed Police Officers).Gunshot Residue (GSR) can also be referred to as Firearms Discharge Residue (FDR) or Cartridge Discharge Residue (CDR).

Hairs

Physical contact between people may result in hairs (head, body or pubic hair) being transferred from one person to another. Hairs may also be found at a crime scene, for example adhering to woodwork or glass at the point of entry in a burglary.

Hairs are identified and compared using microscopy. If the root and sheath material is still adhering to the hairs, they can be subject to forensic hair DNA testing and compared to a reference sample from a subject. Hair trace evidence examination can also provide information about racial origin.

If a DNA profile is obtained from hair then it may uniquely identify a person. Otherwise, it is more likely that hair comparison will only suggest that the hair is more probably from one person rather than another.

 

Fibres

Forensic fibre analysis can provide information about whether there has been physical contact between people, or whether someone was present at the crime scene.

Physical contact between people may result in fibres being transferred (transference) from the clothing of one person to another. In addition, fibres from someone's clothing may be left at a crime scene, for example adhering to woodwork or glass at the point of entry in a burglary.

The recovery of fibres must take place under carefully controlled conditions by a forensic trace evidence expert to avoid inadvertent transfer of fibres between the suspect's and the victim's clothing. A forensic fibre comparison is undertaken using microscopy and chemical analysis.

The strength of evidence depends upon the number and type of fibres recovered. 

Damage

This is the examination of items to interpret appearance, condition, damage/wear and cause of any damage/wear. Comparison of items to reference items or correlate damage to range of items.

Toolmarks / Instrument Marks

This involves the testing of marks and impressions for physical fit, manufacturing marks, defects, damage etc. and comparison of the instrument marks to a crime scene or recovered object. 
 

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