Fibres and Hairs are considered to be traditional forensic trace evidence and with the rise of DNA profiling have fallen from favour. However many significant cases in recent times have largely relied upon such evidence.
Textile Fibre Examinations
We are surrounded by textile surfaces made from fibres, including clothing and soft furnishings. These fabrics lose, or shed, fibres from their surfaces and during normal daily life fibres are routinely and unavoidably transferred between surfaces. For example, when driving a car, fibres might be transferred between the fabric of the clothing worn by the driver and the fabric of the car seat. These fibres are usually only a few millimetres in length and therefore mostly invisible to the naked eye. Transferred fibres will be retained on a surface for variable lengths of time depending on the nature of the surface and what happens to the surface afterwards.
Recovery and analysis of fibres
Fibres can be recovered from surfaces using several techniques, the most common of which is ‘taping’. This involves the use of clear sticky tape, similar to Sellotape, the sticky surface being used to recover fibres from the surface of interest.
By using microscopic examination and a series of analytical tests, fibres which may appear visually similar can often be distinguished. The constituent fibres of a ‘donor’ textile surface (for example an item of clothing) can be compared with fibres recovered from a surface which is alleged to have been in contact with it (for example a weapon, a car seat or another item of clothing). The expert will assess the evidential significance of a set of ‘matching’ fibres within the context of the case scenario. In some cases, it is also relevant to consider whether the absence of matching fibres is of significance, where a transfer would have been anticipated.
The evidential value of fibres
Fibres can provide strong evidence to support that contact between surfaces has taken place and, unlike DNA, potentially, a time frame within which that contact is likely to have occurred. The type of cases involving textile fibre transfers is wide, ranging from fibres recovered from the point of entry at a burglary to a murder case where the clothing of the victim might be examined for fibres from their assailant.
Similar to DNA, fibres can be transferred as a result of a direct contact between surfaces or via an intermediate surface, often called secondary transfer. Consideration must be given to how recovered fibres might have been transferred and whether there has been any opportunity for contamination.
Examination of hairs is generally carried out to determine from whom a hair might have come. Whilst DNA analysis of hairs can sometimes assist, the examination and comparison of the visual appearance of hairs might also be of value. Whilst head hairs are most commonly considered, hairs from other body areas, such as pubic hairs, may be of significance in sexual offence cases.
Hairs as a source of DNA
Hairs can provide a source of DNA, but generally a root is required in order to attempt DNA profiling and success in obtaining a profile can be fairly limited. There are specialist mitochondrial DNA tests that can be performed on the shaft of hairs, but these provide limited discrimination and the results are not comparable with the National DNA Database.
Microscopic analysis of hair
The microscopic comparison of hairs is now rarely used evidentially in the UK given the generally limited strength of support when a ‘match’ is found. However, microscopic examination can be useful to eliminate an individual as a potential source of a hair.
A range of other potentially significant information can be gained from microscopic hair examinations:
From examination of the hair root it is possible to distinguish between hairs that have been forcibly removed rather than naturally shed.
Identification of hairs that have been dyed may provide a more valuable evidential link, particularly where they have been dyed multiple times.
In suspected arson cases, hairs (both head hairs and body hairs from hands and arms) may also be examined for heat damage which is often not visible to the naked eye.
Where hairs from animal sources are of significance it is sometimes possible to determine the type of animal from which the hairs have come.
Fibres and Hairs Expertise
Both fibres and hairs expertise are now considered to be niche, specialised areas of forensic evidence.
Background data is generally limited, and casework experience is critical in evaluating the significance findings. The laboratory work is time consuming and expensive to commission which often deters police investigations with limited budgets. Police forces may screen items, to decide which might be suitable sources for transferred fibres, and subsequently restrict the fibre examinations carried out, not necessarily giving a full picture. Hair examinations are rarely considered.
It is therefore vital to choose an experienced fibre or hair expert who can review the work that has been carried out, establish what further work might assist and consider the limitations and significance of the findings in the case context.
Our expert, Kerri Allen, has carried out fibre and hair examinations for more than 30 years. Contact Kerri for advice and to discuss how she may assist with your case.