The individuality of fibres used to provide forensic evidence--not all blue polyesters are the same.

Fibres used in forensic casework suffer from a disadvantage common to other forms of trace evidence--it is not possible to state with absolute certainty that they originate from a specific source. Target fibre studies, population studies and research on 'blocks of colour' have effectively demonstrated the polymorphism of textile fibres (particularly man-made ones) and have shown that when a fibre is believed to have a specific putative source, the chance that it has originated from a different source purely by coincidence is extremely remote. A study by Houck MM (Houck MM, Inter-comparison of unrelated fibre evidence. Forensic Science International 2003; 135: 146-149) has shown that no coincidental matching fibres were recovered from items of clothing examined in 20 unrelated crimes. The study involved over two million comparisons. This work goes a step further, and using the example of blue polyester fibres shows that even within a very narrow segment of the whole general fibre population, many examples of a specific colour/type of man-made fibre taken from random sources can be compared and the chance of any two being the same is very low. These studies should help to show the specificity and value of transferred fibres in providing forensic evidence.