The evidential value of black cotton fibres

Forensic scientists are faced with the problem of estimating the frequency of cotton fibres recovered in casework, in relation to those in the general population. One way of doing this is to consider the degree of spectral variation that occurs within a "block of colour". When a spectral pattern occurs very frequently, the evidential value of the fibres may be so low, that it is not worth considering them as target fibres. Using UV-visible range microspectro-photometry (MSP) spectra were recorded from 88 known black cotton dyes and 225 samples of black cotton taken from various textiles. UV-visible spectra originating from sulphur dyes and from the great majority of reactive and direct dyes can be easily recognised. Vat dyes present a little more difficulty. The degree of spectral variation and consequent discriminating power of MSP varied according to the dye class, from 0.13 for sulphur dyes to 0.93 for reactive dyes. From 99 textiles dyed with reactive dyes, the spectra could be divided into at least 40 varieties showing that these fibres have a high degree of individuality. Within the few direct dyes (11.5%) that were encountered, one basic spectral form predominated, but a number of minor variations were observed. Spectral information below 400 nm (UV-range) is important for making distinctions and is critical in the case of direct dyes.     

A study to investigate the evidential value of blue gel pen inks

The aim of this project was to investigate the evidential value of blue gel pen inks in Europe. For this purpose, 33 blue gel pen inks, of different brands and models, representative of those available on the European market at the time of the study, were analyzed using three techniques: filtered light examination (FLE), Raman Spectroscopy (RS), and scanning electron microscopy (SEM). First, after visual examination (naked eye and stereo microscope), it was possible to classify the 33 inks into three groups described as: milky, metallic, and normal. This paper describes in detail the results obtained for the normal gel pen group. The ability of the techniques to discriminate gel inks between and within brands varied. The results indicated that RS and SEM were more discriminating than FLE. The greatest degree of differentiation was achieved when using a combination of RS and SEM techniques (discriminating power = 0.91). This study also highlights some problems concerning the identification of the brand of a gel pen from a written text.     

A study to investigate the evidential value of blue and black ballpoint pen inks in Australia

The aim of this project was to investigate the evidential value of blue and black ballpoint pen inks in Australia. For this purpose, 49 blue and 42 black ballpoint pen inks, of different brands, models and batches, representative of those ballpoint pens available on the Australian market at the time of the study, were analysed by three techniques: filtered light examination (FLE); reflectance visible microspectrophotometry (MSP); and thin-layer chromatography (TLC). The results showed that the power of the individual techniques to discriminate inks between and within brands, models and batches varied, the most informative techniques being TLC>FLE>MSP. The greatest degree of differentiation was achieved when using a combined sequence of techniques, the discriminating power being 0.99 and close to 1 for blue and black inks, respectively (different brands and models). In respect to the discrimination between different batches of a same brand and model, it was shown that 14 out of the 33 pairs compared could be discriminated. Overall, this study confirmed the high value of the examination of inks when applied to ballpoint pens available in Australia, especially when a combined sequence of techniques is applied.     

Adhesive tape analysis: establishing the evidential value of specific techniques

This study investigated the evidential value of specific methods of analysis for packaging tapes and clear adhesive tapes available in Australia. Fifty-eight adhesive tapes were analyzed using a wide range of optical, physical, and chemical techniques. The results were collated for the purpose of creating an Australian database of adhesive tapes, which would be of assistance in criminal investigation. Each technique was evaluated for its discriminating power, both for comparative purposes and for the identification of adhesive tapes by comparing unknown samples with the database. The combined discriminating power of the techniques applied is very high. It is possible to individually identify the source of an unknown adhesive tape sample in many instances by searching the database. It is also possible to form an opinion on the significance of a failure-to-discriminate result in comparative casework. Further work is still needed to expand and update the database, as well as compiling data on the relative market share of various products.     

Enzymatic extraction of dyes for differentiation of red cotton fibres by TLC coupled with VSC

The purpose of this work was to assess the usefulness of thin layer chromatography (TLC) for discriminating single cotton fibres dyed with red reactive dyes. An effective enzymatic extraction procedure with the use of cellulase for the red reactively-dyed cotton fibres was developed and used for the discrimination of fibres derived from 21 garments purchased commercially. Discrimination of the fibres relied on the separation of the extracted dyes by thin layer chromatography (TLC). Four eluents were used to develop the plates with the extracted dyes, and the obtained results were analysed using, among others, video spectral comparator (VSC). Observation of TLC plates in visible, ultraviolet and infrared light allowed unambiguous discrimination of 5 and probable discrimination of 6 of the 21 fibres tested. The remaining fibres were divided into several groups. Comparison of the acquired results with those obtained for the same examination material by standard non-destructive methods used in forensic fibres examinations (transmitted light microscopy, fluorescence microscopy, UV–Vis microspectrophotometry and Raman spectroscopy) has shown that efficiency in fibres differentiation is similar for all methods. TLC coupled with VSC was even found to be more effective in differentiation of red cotton fibres. The chemometric analysis was helpful to discriminate dyed cotton fibres, characterized by very similar colour.     

Raman spectroscopy and the forensic analysis of black/grey and blue cotton fibres Part 1: investigation of the effects of varying laser wavelength

Raman spectroscopy was investigated to determine the optimal conditions, mainly laser wavelength/s, for the analysis of the commonly encountered black/grey and blue cotton fibres dyed with reactive dyes. In this first part, a single blue cotton fibre, its three dye components, and an undyed cotton fibre were analysed with five different laser wavelengths from two different Raman microprobe spectrometers. The quality of the spectra, fibre degradation and speed of acquisition were used to determine that, under the conditions used, the 785 and 830 nm lasers gave superior results. The 632.8 nm laser wavelengths provided good results with little acquisition time and no spectral degradation. Results indicate that, at least, the major dye component could be identified using Raman spectroscopy.     

The production of colour coordinates from microgram quantities of textile fibres. Part I

This paper describes a method for defining the colour of small samples of textile fibre in terms of its complementary chromaticity coordinates. The coordinates can be calculated from the absorption spectra of solutions of the dye extracted from fibres and use is made of data taken from published tables. Problems arising from this procedure, its significance for the court going officer, and possible future developments are discussed.     

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.     

Fibres used in the construction of car seats — An assessment of evidential value

The evidential significance of car seat fibres has been investigated. Thirty six samples of car seat fabric were examined and the fibres catalogued according to their morphology and characteristics. The majority of car seat fibres were black or grey thick polyester fibres that were either dyed or pigmented. The MSP spectra produced were unlike those usually obtained from black or grey polyester fibres used in clothing. Tapings taken from car seats were examined for car seat fibres, various types were found showing that these fibres are expected to shed from the fabric albeit in low numbers, unless the vehicle is older. No fibres that matched the samples of the car seat fabric were found on the tapings of the car seats. One hundred garments were examined for car seat fibres, 10% of garments had populations of such fibres present and 41% had at least one car seat fibre present. None of these fibres matched the samples of the car seat fabric or those from the car seat tapings.     

Raman spectroscopy and microspectrophotometry of reactive dyes on cotton fibres: Analysis and detection limits

A collaborative study on Raman spectroscopy and microspectrophotometry (MSP) was carried out by members of the ENFSI (European Network of Forensic Science Institutes) European Fibres Group (EFG) on different dyed cotton fabrics. The detection limits of the two methods were tested on two cotton sets with a dye concentration ranging from 0.5 to 0.005% (w/w). This survey shows that it is possible to detect the presence of dye in fibres with concentrations below that detectable by the traditional methods of light microscopy and microspectrophotometry (MSP). The MSP detection limit for the dyes used in this study was found to be a concentration of 0.5% (w/w). At this concentration, the fibres appear colourless with light microscopy. Raman spectroscopy clearly shows a higher potential to detect concentrations of dyes as low as 0.05% for the yellow dye RY145 and 0.005% for the blue dye RB221. This detection limit was found to depend both on the chemical composition of the dye itself and on the analytical conditions, particularly the laser wavelength. Furthermore, analysis of binary mixtures of dyes showed that while the minor dye was detected at 1.5% (w/w) (30% of the total dye concentration) using microspectrophotometry, it was detected at a level as low as 0.05% (w/w) (10% of the total dye concentration) using Raman spectroscopy. This work also highlights the importance of a flexible Raman instrument equipped with several lasers at different wavelengths for the analysis of dyed fibres. The operator and the set up of the analytical conditions are also of prime importance in order to obtain high quality spectra. Changing the laser wavelength is important to detect different dyes in a mixture.     

Statistical evaluation of the evidential value of human hairs possibly coming from multiple sources

A concept of the mathematical evaluation of human hair evidence is derived. This concept can be realized in a special computer program, the output of which is an incrimination probability. The problems of not knowing the true number of sources and the correct partition of hairs corresponding to their sources are solved from the point of view of avoiding an unjustified incrimination.     

The evidential value of distorted and rectified digital images in footwear imprint examination

The procedure for forensic photography requires that the film plane be parallel to the taken image. Another procedure must be used when the print is located on reflecting surfaces such as vehicles, or faint marks on porous surfaces. Examination was made of the evidential value of footprint images received from the scene or taken deliberately at an angle out of proper perspective (i.e., the lens axis is not perpendicular to the target plane). An artificial target was prepared and photographed from several lens axis angles ranging from 10 degrees to 85 degrees to the perpendicular, and then rectified using the Adobe Photoshop Version 7.0. It was found that at angles less than 40 degrees , the shape and location of all the individual characteristics were similar enough in comparison to the original image. In images taken at higher angles, the original image could not be adequately restored. The full potential of this image, therefore, could not be achieved after rectification. The results of this study show that the images of a footprint taken at an angle less than 40 degrees , preserve the evidential value of the unique characteristics.     

An evaluation of the Maxcan fibre finder version 3.3 on cotton fibres

The Maxcan fibre finder system is a product of Cox Analytical Systems, Sweden, and has been developed for the primary purpose of searching for fibres on tape lifts. This paper evaluates the ability of the Maxcan system to search for different fibre types and colours under varying conditions. The system performed effectively in most situations, although it did have problems with some search combinations that a human operator would also find difficult in a manual search. The Maxcan system has the added advantages of being objective, consistent and able to do large batch searches unattended. These attributes make it very useful where a large number of tapes need to be searched in casework and also in research where large quantities of data need to be gathered within a reasonable time.