A pilot study to determine the background population of foreign fibre groups on a cotton/polyester T-shirt.

The interpretation of fibre evidence requires an assessment of the value inherent in the number of matching fibres. In a Bayesian framework the probability that a group of x fibres would be present on a garment by chance needs to be assessed (Sx). Accordingly, a pilot study of the total foreign fibre population on a small number of garments was undertaken. The number of coloured fibres found on six white T-shirts after each one was worn for one day was counted. The T-shirts were found to contain between 9,108 and 13,925 coloured foreign fibres. All of the coloured fibres from one of these T-shirts were microscopically examined to record their colour, width and length, and to classify them as either cotton, wool, synthetic, silk or miscellaneous. Pair-wise comparisons of similar fibres were then performed to determine the number and size of the groups of foreign fibres present on the T-shirt. These results add to the published information regarding the background foreign fibre populations on clothing and other items. This knowledge should assist the forensic fibre analyst when using a Bayesian framework to interpret fibre cases.