Trace evidence such as paint, glass and fibres, is commonly encountered in a wide range of case types.
Glass can be transferred onto an individual’s clothing and hair as the result of the breaking of a window or, for example, during an assault with a drinking glass. Subsequent recovery of the fragments of glass and comparison against reference samples from the control (e.g. broken window) can establish whether or not the glass fragments could have come from the broken glass object. The interpretation of the significance of the findings will depend upon a number of factors including how common the glass in question is and the number of matching and non-matching fragments that have been recovered.
Similarly, paint can be transferred onto a tool, for example, when it is used to force open a painted window frame and, if the tool itself is painted, there can be two-way transfer of paint from the tool to the window frame. In such a situation, there is also the potential to compare the impression left by the tool with the tool itself to establish whether it could have made the tool mark. Paint is also transferred in other situations, for example in a road traffic collision, paint from one vehicle can be transferred to another vehicle or object that has been in collision with the vehicle. Microscopic and chemical comparison of the paint samples, including the various layers of paint that may be present, can establish whether or not the paint could have come from a particular source such as a tool or vehicle.
Textile fibres are used to make items of clothing as well as furnishings and other items such as ropes and bags. Items shed textile fibres to different degrees but where they do shed fibres, any contact with a receptive surface will lead to the transfer of fibres between items. Recovery and subsequent comparison of textile fibres can help establish whether, for example, two garments have been in contact with each other or whether a garment has been in contact with another surface such as a chair or car seat. Once fibres have been deposited on another garment, they are lost relatively quickly during routine wear and, therefore, the number of fibres recovered can be a significant factor. Fibres can also be transferred during “secondary transfer”. For example, fibres transferred from one garment to a chair can subsequently be transferred to another garment that comes into contact with the chair. Interpretation of the significance of finding matching fibres is therefore critical and will depend upon a number of factors including how common the fibres in question are.