Following the experiment, the black top of the recipient was photographed using UV-imagery techniques to determine the number of fibres transferred. The results of the study proved that not only can textile fibres actually transfer between garments without physical contact, but they can do so in relatively high numbers.
Often in a criminal case the finding of just a few fibres can be considered significant. So the fact that up to 66 fibres were transferred in a single experiment, was considerably higher than anticipated. That said, not all garments we tested transferred fibres to the same extent. We found the type of fibres the donor garment was constructed from and its ability to shed those fibres was key in contactless fibre transfer. The type of clothing worn by the recipient also impacted transfer, as did the movement of people and the opening or closing of the elevator doors.
Each category is carefully considered, as any evidence is potentially incriminating. By matching fibers at the scene of a crime to items belonging to a suspect, investigators are able to place individuals at a crime scene. The problem with fiber evidence particularly when discussing clothing is that cloth items are generally mass produced.
The only way determine that a fiber came from a particular piece of cloth is to know without a doubt that the item is unique, or to actually witness the transfer of the fibers.
That said, the likelihood that a garment with the exact same color, texture, weave, and material would be at a crime scene is astronomically low. In a property crime where a tool is used to break into a building, paint transferred to or from the tool can connect the tool to the location. Analyzing automotive paint can identify the make, model and sometimes the year of a vehicle. Collection: To collect paint, investigators document the scene, then peel off, or excise, small amounts of paint from the source, being careful to gather all layers.
Samples as small as one square millimeter can be used for testing. For a car crash scene, paint samples from the point of contact would be photographed, collected and stored in such a way as to protect the edges for further examination. This is particularly important when examining for fracture matches.
Paint samples are typically collected by scraping small sections down to the metal or original surface or using tweezers to collect chips already dislodged. Most large laboratories or laboratory systems have a trace evidence section. Analysts have a variety of backgrounds, but most require a degree in a natural science with additional certification or additional study in chemistry, particularly if the primary degree is not in chemistry.
Certification is generally conferred on an individual who has achieved specific education, training, experience and performance on competency tests as designated by the certifying organization. Some areas of trace evidence have individual certification programs, which are facilitated by professional associations and boards.
Since trace evidence covers a wide variety of subcategories, there is similar variety in the testing that is performed. Specialized testing may be done outside of the local laboratory at regional or national facilities.
The type of test performed and the range of information provided vary by the type of evidence tested. For example, analysis of a strand of hair may yield information on the race and general health of the donor, while analysis of a paint sample would likely yield the manufacturer of the paint and its commercial use.
That is why collection and packaging of fiber evidence is important. Fiber-plastic fusion can occur between the clothing of the occupant and interior surfaces of the vehicle which are made of thermoplastics. During an impact, parts of the garments can be rubbed under high pressure against the surface of the vehicle which then causes frictional heat. This, in turn, causes local melting of the thermoplastic material.
During this contact, fibers from the garment can be transferred and become embedded into the softened plastic. It is the plastic material that is actually melting and not the fibers.
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