Forensic Examination Of Fibres Research Articles

Forensic examination of different textile fibres using UV- Vis spectroscopy

Objective: The purpose of this study is to forensically examine different textile fibres using UV/visible spectroscopy. Methodology: Five different fibre types of ten different local brands have been analyzed using uv-vis spectroscopy.Each fibre was dissolved in 3ml of chloroform and were kept overnight for the extraction of dye from the fabric. Then the extracted dye sample was analysed in UV-vis spectroscopy. Results: The results demonstrated that concentration of dye was higher in cotton samples and lower in polyester samples. The mean concentration of dye in cotton samples were (443.0-846.5) nm, polyester (402.0-656.0) nm, jute (484.0-673.5) nm and silk (402.0-661.0) nm respectively. But in wool samples dye did not get extracted. It may be because in wool keratin is present and these materials differ only by the presence of crysteine in wool, which were more intense for wool fibres. Conclusion: There has been a considerable amount of importance of fibre evidence in criminal investigations. Investigating the various dyes utilised to colour textile fibres can provide extra information in the process of determining the chemical compounds of the fibre. In the forensic study of fibres, colour discrimination relies heavily on UV/visible spectroscopy.

Forensic examination of textile fibres using Raman imaging and multivariate analysis

Vibrational spectroscopic techniques have shown to be highly suitable for the identification and comparison of textile fibres and clothing fabrics. On the other hand, new chemical imaging modes based on these spectroscopic techniques are becoming useful in multiple fields. This is particularly important to, for instance, chemically visualize and screen different samples including forensic evidence (crime scene investigation), chemical and food products (quality control), biological tissues and living beings (medical imaging), among others. This study explores the forensic examination and selective chemical visualization of textile fibres and clothing fabrics using Raman imaging. Four experiments were performed, which were focused on the screening of (i) white different materials made of 100 % cotton (gauze, cotton wool, t-shirt, and swab), (ii) polyester and cotton fabrics evidence of the same colour, (iii) five different coloured cotton fabrics, and (iv) textile fibres of different materials (acrylic, cotton, nylon, polyester, and silk). Several methods of multivariate chemometric analysis including principal component analysis (PCA), multivariate analysis of variance (MANOVA), and multivariate curve resolution (MCR) were applied to enhance the limited visual comparison of the spectra accomplished with the unaided eye. The results evidenced the suitability of Raman imaging to statistically discriminate textile fibres and fabrics due to the chemical composition of both the clothing material and the dyestuff.

A comparative investigation of two handheld near-ir spectrometers for direct forensic examination of fibres in-situ

Fibres comparison in forensic science play a significant role in solving different crimes. Worldwide the most common textile fibre materials (fabrics) found at crimes scenes are cotton, polyester, denim, polypropylene, polycotton, and viscose. These fabrics are the focus of this study. The textile fabrics were examined by two handheld near-infrared (NIR) spectrometers, SCIO® by Consumer Physics and NIRscan Nano by Texas Instruments, for in situ comparisons of fibres, demonstrating capability at a crime scene. Spectral differences were apparent between both spectrometers due to the complementary wavelengths, SCIO interrogates the third overtone region (740–1070 nm) and NIRscan Nano interrogates the first and second overtone regions (900–1700 nm). A SCIO and NIRscan Nano data were pre-processed to eliminate noise and smooth the data for input to machine learning classifiers. The data were pre-processed and modelled by PRFFECTv2 software, and showed good predictive accuracy, with accuracy, sensitivity and specificity in the range 78–100 % for the best binary classification models (one class versus others) and within the range 65–100 % for the best multi-class classification models. This paper presents for the first time the use of small handheld spectrometers coupled with the Random Forest (RF) algorithm to classify fibre material for forensic comparison purposes in a fast, rapid, and non-destructive manner that is ideally suited for direct analysis at the crime scene.

Probability-Based Validation of the Forensic Method "Microscopic Analysis of Textile Fibers"

The results of validation of the method “Microscopic analysis of textile fibers” used in forensic fiber examination are presented. An attempt is made to estimate reliability of testing of this method numerically by the proportions of right and false results and credibility ratio.The testing method under consideration consists in establishing a set of external characteristics of natural and chemical textile fibers: color, peculiarities of coloration, morphological features, presence/absence of a matting agent. These generic characteristics are used in forensic textile analysis. As the objects of testing fiber samples from comparative collection of a forensic fiber laboratory were used. Four experts participated in the experiment independently examining eleven fiber samples by eleven external characteristics for a week.A low (2,2 %) rate of false results in relation to the total number of tests was established as well as the low (less than 3,0 %) rate of each expert’s false results. The probability of the right results of characteristics’ assessment is 30 times higher than the probability of false results.The results of the experiment permit the conclusion that the method is suitable to be used in forensic fiber examination when dealing with various tasks: classification, identification, situational and diagnostic.

A sensitive HPLC-MS/MS method for the analysis of fiber dyes

Textile fibers are frequently encountered as trace evidence. The identification and comparison of fibers is very important for case investigation, and an important aspect of forensic fiber examination is the characterization of fiber dyes. Fibers recovered at crime scenes are often very small and contain multiple dyes, which require a high demand for the sensitivity and separation efficiency of dye analysis methods. The combination of high performance liquid chromatography and tandem mass spectrometry (HPLC-MS/MS) is a highly selective and sensitive analytical method that can be useful for the characterization of dyes. A sensitive HPLC-MS/MS method is described here to analyze fiber dyes in different classes (acid, basic, direct, reactive, and disperse). Acetonitrile/water addicted with 0.1% acetic acid was utilized as the mobile phase. Under the optimized conditions, the limit of detection (LOD) for different dyes reached 0.01–16.7 ng/mL in Multi Reaction Monitor (MRM) mode. The described method is sensitive enough to analyze single fibers with a length of a few millimeters or less, which makes it suitable for forensic analysis.

Application of dye analysis in forensic fibre and textile examination: Case examples

Seven cases and a quality assurance test are presented. In these cases, fibres or textiles submitted for investigation were analysed by HPLC–DAD–MS to identify the dyes present. The cases presented illustrate that it is possible to identify textile dyes in fibre traces recovered for forensic analysis. The results show that a mixture of dyes is present in all textiles investigated, except one sample that was taken from a manufacturer dye shade card. It is concluded that dye analyses improves the evidential value of forensic fibre examinations, as it becomes possible to distinguish textiles that are different in dye chemistry, but have a similar colour. In addition dye analysis makes the examination more robust, as it becomes possible to attribute colour differences between samples to identical dyes (mixed in different ratios) or to chemically different dyes.

Using a forensic science approach to minimize environmental contamination and to identify microfibres in marine sediments

There is growing evidence of extensive pollution of the environment by microplastic, with microfibres representing a large proportion of the microplastics seen in marine sediments. Since microfibres are ubiquitous in the environment, present in the laboratory air and water, evaluating microplastic pollution is difficult. Incidental contamination is highly likely unless strict control measures are employed. Here we describe methods developed to minimize the amount of incidental post-sampling contamination when quantifying marine microfibre pollution. We show that our protocol, adapted from the field of forensic fibre examination, reduces fibre abundance by 90% and enables the quick screening of fibre populations. These methods therefore allow an accurate estimate of microplastics polluting marine sediments. In a case study from a series of samples collected on a research vessel, we use these methods to highlight the prevalence of microfibres as marine microplastics.

Towards source level evaluation of the evidential value of fibre examinations

This paper aims to provide the first steps towards a numerical source level evaluation of fibre evidence. For that purpose, likelihood ratio equations are derived for four generic scenarios, in which the source frequency, the number of references and trace types investigated, and the number of matches vary. Previous experimental studies into the evaluation of fibre evidence are reviewed and we demonstrate how the results of these studies, as well as other data, can be used to evaluate the derived equations for the four scenarios. Evaluation is not straightforward and requires a number of assumptions. This is mainly because the relevant population under consideration in a specific case cannot be sufficiently evaluated. In addition, the subjective match-criterion in current forensic fibre examinations makes it impossible to implement a good evaluation of the within-variation of samples. As a result, the discrimination power, currently calculated for discrimination studies, is only valid for samples with negligible heterogeneity. We conclude that reporting a numerical evidential value for forensic fibre examinations is not yet feasible as the data are available for only a few types of fibres and cannot be used without several assumptions. We propose a number of developments that are required to improve the accuracy and numerical analysis.

The use of linear dichroism in forensic fibre examinations — Part 6. Validation and practical aspects of MSP-PPL

This paper summarizes the results of previous work on the microscopic observation of linear dichroism found in dyed fibres (polyesters, polyamides, wool, silk, cotton, viscose, acrylics and acetates) and in pigmented fibres as well as the measurements on these fibre classes using microspectrophotometry with plane polarized light (MSP-PPL). The validation of this method is discussed and a practical tool is proposed for comparing fibre traces with control fibres. The limitations and strengths of this method are also revised.

Dichroism measurements in forensic fibre examination

A number of pigmented fibre samples were examined with plane polarized light on their dichroic behaviour by optical light microscopy (OLM) and microspectrophotometry with plane polarized light (MSP-PPL). It was found that about half of the samples show a strong dichroic effect and another 20% have a weak dichroism. Both regular (80%) and inversed dichroic effects (20%) occur. The dichroic characteristics of pigmented fibres can be compared to these of sheet polarizers. It is suggested that the dichroic behaviour of pigmented fibres depends strongly on the crystal structure (shape of the pigment grains) and the draw ratio (orientation of the polymer chains).

Dichroism measurements in forensic fibre examination. Part 4—dyed acrylic and acetate fibres

A number of dyed acrylic and acetate fibre samples were examined with plane polarized light on their dichroic behavior by optical light microscopy (OLM) and microspectrophotometry with plane polarized light (MSP-PPL). It was found that most of these low birefringent fibres possess weak dichroic effects that are very hard to observe with microscopy. However, using MSP-PPL, the linear dichroism could be measured. A comparison between the dichroic effects found for the same disperse dyes on triacetate (TrAc), diacetate (Ac), polyester (PES) and polyamide (PA) shows that the linear dichroism follows the order: PA>PES >>TrAc, Ac.

Dichroism measurements in forensic fibre examination

A number of dyed cellulosic fibres were examined with plane polarized light on their dichroic behavior by microscopy and microspectrophotometry (MSP-PPL). Significant dichroic effects (mostly hypochromic effects and hypsochromic bands shifts) were reported. The effect is related to the chemical structure: some dye structures always possess dichroism (azo, stilbene, thiazole and oxazine), some dyes demonstrate sometimes dichroic effects (anthraquinoid, indigoid) while other structures never demonstrate dichroic effects (sulphur, diphenylmethanes, triarylmethanes, phthalocyanines). In some cases a different dichroic behavior was found for the same dyes applied on cotton and on viscose.

The Effect of Ionizing Gamma Radiation on Natural and Synthetic Fibers and Its Implications for the Forensic Examination of Fiber Evidence*

Circumstances of criminal activities involving radioactive materials may mean fiber evidence recovered from a crime scene could have been exposed to materials emitting ionizing radiation. The consequences of radiation exposed fibers on the result of the forensic analysis and interpretation is explored. The effect of exposure to 1-1000 kGy radiation doses in natural and synthetic fibers was noticeable using comparative forensic examination methods, such as optical microscopy, microspectrophotometry, and thin-layer chromatography. Fourier transform infrared spectroscopy analysis showed no signs of radiation-induced chemical changes in any of the fiber structures. The outcome of the comparative methods highlights the risk of "false negatives" associated in comparing colors of recovered fibers that may have been exposed to unknown radiation doses. Consideration of such results supports the requirement to know the context, including the environmental conditions, as much as possible before undertaking a forensic fiber examination.

Dichroism measurements in forensic fibre examination. Part 2 — Dyed polyamide, wool and silk fibres

A number of dyed polyamide, wool and silk samples were examined with plane polarized light on their dichroic behavior by optical light microscopy (OLM) and microspectrophotometry with plane polarized light (MSP-PPL). It was found that most of these acid dyed peptidic fibres possess dichroism, but these are weaker than the effects previously described for polyester fibres. The small effects may be not observed, especially for wool, but these can be measured using MSP-PPL. In the three peptidic fibre classes, for the first time, a so called "inverse dichroism" is observed which appears in the absorption spectra as a hyperchromic effect.

Dichroism measurements in forensic fibre examination

One hundred and twenty dyed polyester samples were examined with plane polarized light on their dichroic behaviour by optical light microscopy (OLM) and microspectrophotometry in the visible range (MSP Vis). It was found that most of these disperse dyed polyester fibres possess a strong dichroism, which fall into two broad categories. Either a decrease of intensity (hypochromic effect) or a change of hue (hypsochromic or bathochromic shift of absorption bands) is noted. These dichroic effects are related to the orientation of the dye structure with respect to the polymer chains.

Forensic evidence in apparel fabrics due to stab events

Stab injuries and fatalities have been reported to be the most common crimes of violence in several countries, particularly in those where access to firearms is restricted [J.M. Taupin, F.-P. Adolf, J. Robertson, Examination of damage to textiles, in: J. Robertson, M. Grieve (Eds.), Forensic Examination of Fibres, CRC Press, United States of America, 1999, pp. 65–87; A.C. Hunt, R.J. Cowling, Murder by stabbing, Forensic Sci. Int. 52 (1991) 107–112; D.A. Rouse, Patterns of stab wounds: a six year study, Med. Sci. Law 34 (1994) 67–71]. Analysis of damaged apparel may provide important information about the cause of death and the events leading up to and after the victim's final moments [M.T. Pailthorpe, N.A.G. Johnson, The private forensic scientist and the criminal justice system, in: D. Biles, J. Vernon (Eds.), Private Sector and Community Involvement in the Criminal Justice System: Conference Proceedings, vol. 23, Australian Institute of Criminology, Wellington, 1994, 231–240]. A high proportion of stab wounds occur in the chest and as this area is generally clothed many sharp force cases involve damage to fabrics [J.M. Taupin, F.-P. Adolf, J. Robertson, Examination of damage to textiles, in: J. Robertson, M. Grieve (Eds.), Forensic Examination of Fibres, CRC Press, United States of America, 1999, pp. 65–87; A.C. Hunt, R.J. Cowling, Murder by stabbing, Forensic Sci. Int. 52 (1991) 107–112; D.A. Rouse, Patterns of stab wounds: a six year study, Med. Sci. Law 34 (1994) 67–71]. The structural stabilisation and degradation of fabric due to laundering significantly alters fabric properties [S.E. Gore, R.M. Laing, C.A. Wilson, D.J. Carr, B.E. Niven, Standardizing a pre-treatment cleaning procedure and effects of application on apparel fabrics, Text. Res. J. 76 (2006) 455–464], yet the effect of such on severance morphology does not appear to have been investigated. In this work the effect of blade type (hunting knife, kitchen knife, screwdriver) on new and laundered apparel fabrics was investigated. Two approaches were used (i) a human participant trial, and (ii) guided drop testing (using an impact rig). Force–time plots from the human participant trials were matched to those from the impact rig. Information on severance morphology was obtained using visual analysis techniques. Blades could be differentiated and directionality estimated by observing differences in severance shape and size, the degree of fabric distortion, the position of severed yarn ends, loop snippets, curled yarns, planar array and the morphology of fractured fibres. Fabric construction had a visible effect on severance morphology. Pre-impact degradation via laundering hindered the ability to link fractured fibre ends to a source of damage by altering morphology and increasing the variability. The correlation between blade height and severance length was weak, attributed to elastic deformation and recovery. The impact rig was a valuable tool in the reconstruction of textile damage. Damage was consistent when inflicted using a human participant trial and the impact rig, although more variable in the former. The advantage of the impact rig lies in the ability to produce a severance typical of the blade in question, under controlled conditions, in a reproducible manner.

Morphological changes in textile fibres exposed to environmental stresses: Atomic force microscopic examination

The ability of the atomic force microscope (AFM) to investigate the nanoscopic morphological changes in the surfaces of fabrics was examined for the first time. This study focussed on two natural (cotton and wool), and a regenerated cellulose (viscose) textile fibres exposed to various environmental stresses for different lengths of times. Analyses of the AFM images allowed us to measure quantitatively the surface texture parameters of the environmentally stressed fabrics as a function of the exposure time. It was also possible to visualise at the nanoscale the finest details of the surfaces of three weathered fabrics and clearly distinguish between the detrimental effects of the imposed environmental conditions. This study confirmed that the AFM could become a very powerful tool in forensic examination of textile fibres to provide significant fibre evidence due to its capability of distinguishing between different environmental exposures or forced damages to fibres.

Automotive flock and its significance in forensic fibre examinations

The interiors of fifty eight vehicles were examined and samples were taken. All vehicles had samples of flocked material in their interiors. Flocked material was found on the window channels, window frames, door edges and in glove compartments or central console compartments. The majority of flock fibres used in the vehicles examined were carbon black pigmented polyester or nylon. A variety of dyed nylon fibres were also used in the vehicles. The discrimination power of dyed flock fibres used in the interior of vehicles was found to be 0.974. The front seats of these vehicles were examined for loose flock fibres. All vehicles had flock fibres present on the front seats. In the majority of vehicles, flock originating from material in the vehicle's interior was present on the front seats of the vehicle. The number of flock fibres present on the front seats varied greatly from car to car but did not appear to be dependant on the type of seat fabric or on which areas in the car were flocked.

Identifying a suitable mounting medium for use in forensic fibre examination

As the result of a previous study many laboratories have used XAM neutral medium-improved white mounting medium in textile fibre examination for more than 20 years. Due to European Directive 98/79/EC, XAM is no longer available and an alternative needed to be found. A list of desirable properties was formulated and a number of mounting media were tested against this. Entellan New was identified as the best mounting medium, and performed similarly to XAM in all aspects.

Forensic Textile Fiber Examination Across the USA and Europe

Crime laboratories in the USA, who undertake fiber examinations, together with members of the European Fibres Group (plus representatives from Israel, Japan, Canada, and Australia) were surveyed in 1994 and 1995, respectively, and asked to provide subject-specific information relating to personnel, equipment, training, quality control, and techniques available. The information obtained showed that generally more fiber casework is carried out in Europe than in the USA. Most laboratories are quite well equipped but those in Europe seem to be able to obtain more state-of-the-art instrumentation. Proficiency testing and peer review is accepted practice worldwide. Americans appear to update fiber collections on a more regular basis than Europeans but both keep literature up to date. Contamination is a major issue, as with all areas of trace evidence. The results from the survey suggest that minimum standards are clearly not always being observed. Careful consideration also needs to be given as to whether legitimate contact could have occurred prior to an offense being committed. The standard of forensic fiber examination worldwide is generally high. With laboratory management continuing to support the work of the Scientific Working Group for Materials and the European Fibres Group and by instigating "best practice" as set out in their guidelines, standards should continue to improve.