Forensic Textile
Forensic Textile Science provides an introduction to textile science, emphasizes the terminology of the discipline, and provides detailed coverage of how textile damage analysis can be used in forensics. Part One introduces textiles and their role in forensics, including chapters on fibers, yarns, fabrics, clothing types and construction, and household textiles. Part two covers the analysis of textile damage in a forensic context. Key topics include textile degradation and natural damage, weapon and impact damage, textile rupture, and ballistic damage.
Textile damage analysis is an invaluable tool in forensic investigations and can be used to help solve stabbing, shooting, and sexual assault cases. It also has the potential to resolve arson and acid attacks. Here, the literature is explored to review research related to blunt force injuries, stab and slash cuts, the incidence of evidence falsification in sexual assault, projectile injuries, and the effect of decomposition on textile damage, among others. It is clear that there is a dearth of research in this area, but where research has been done, it has been informative and influential. However, there are areas that require further work, including a better understanding of normal wear and tear and the potential for chemical damage to textiles. One area in significant need of further work is the development of a robust explanatory framework.
Forensic fiber analysis
Textile fibers are a key form of trace evidence, and their ability to reliably associate or discriminate is crucial for forensic scientists worldwide. Although fiber composition can be determined using microscopic and instrumental analysis, additional specificity can be obtained by examining fiber color. This is especially important when the bulk composition of the fiber is relatively uninformative, as it is with cotton, wool, or other natural fibers. Such analyzes pose several problems, including extremely small sample sizes, the desire for non-destructive techniques, and the enormous complexity of modern dye compositions. This review will focus on more recent methods for fiber color comparison using chromatography, spectroscopy, and mass spectrometry. The increasing use of multivariate statistics and other data analysis techniques for the differentiation of spectra from dyed fibers will also be discussed.
In recent years, the application of spectral techniques for the identification and discrimination of textile fibers has gradually increased. Micro-spectrophotometry in the ultraviolet-visible range and Raman and Fourier-transform infrared spectroscopy are the main spectroscopic techniques used in the study of textile fibers. At the same time, technology continues to improve and other spectral techniques are emerging in this forensic area.
For Natural Fiber
There are several factors that explain the increased interest in spectroscopic techniques for textile fiber testing. These are non-destructive techniques and only a very small sample is required to develop an analysis. Depending on their nature, the fibers used for textile products such as clothing can be divided into two groups: natural and synthetic fibers. Natural fibers are composed of organic plant or animal tissue or certain minerals, such as asbestos. Synthetic fibers are mainly obtained by chemical processes of varying complexity carried out in the textile industry. Each of these groups covers a wide range of materials with different chemical structures and physicochemical properties. These particularities determine their characteristics relative to the manufacturing process used in the industry to produce garments and other textile materials of commercial interest.
To identify possible adulteration of linen with jute it is necessary to differentiate between linen and jute. Edwards et al found a specific band at 1736 cm-1 was found for the jute sample and another band at 1578 cm-1 for linen. These bands allow distinguishing between both textiles. Keratin is present in both wool and silk. These materials differ only in the presence of cysteine in the wool. This band was the main difference between the Raman spectra of wool and silk in the study of Cho et al. using a laser at 780 nm. Other important differences are the bands at 1234 and 1094 cm-1, which were more intense for silk than for wool fibers. The position and intensity of the amide band vary according to the conformational changes of the keratin molecule. Moreover, intermolecular interactions between dye molecules and glycosidic groups were also observed. Natural fibers presented an irregular morphology that responded to non-homogeneous dyeing. Thus, fabrics made of natural polymers present a lower threshold intensity and further reduce the intensity of the dye absorption band.
For synthetic fiber
Polyester is a generic term that encompasses a variety of textile materials, with PET being the most commonly used synthetic fiber for production. Different subtypes of PET fibers have similar spectral characteristics and their differences can be seen by studying the relative intensities of the bands around 1100 and 350 cm-1. In a real case, melt-end colorless polyester fibers were investigated in a blue denim textile. These fibers were of forensic interest due to their very rare presence in blue jean fabrics. Analysis of the colorless portion of this fiber confirmed PET as a polymer class. Coyle, on the other hand, found that most of the fibers used in car seat construction are black or gray thick polyester. Recovered fibers with higher absorbances at 677 and 538 nm gave spectra similar to Blue Phthalocyanine and Green Phthalocyanine, respectively. Viscose and cotton show similar spectra due to their cellulose structure. Cho reviewed the major spectral differences between the most common nylon subtypes: nylon 6, nylon 6.6, and nylon 6.12. Nylon subtypes 6 and 6.6 are the most widely produced polyamides. Therefore, it is not rare that these were the most present polyamides in areas of forensic interest. Other important differences between the nylon subtypes were the two bands that nylon 6 presented between 1126 and 1062 cm-1, while the 6.6 and 6.12 subtypes had three bands in this spectral region. The C-C-O band extended to about 940 cm-1 represents a specific position for each subtype of nylon. It appeared at 953 cm-1 for nylon 6.6, 948 cm-1 for nylon 6.12, and 932 cm-1 for nylon 6.
Analysis of the fiber color variations
Suzuki, investigated color variations according to variable dye concentration along the garment surface. A small inter-variation of transmission intensity was observed in single wool fibers and a relatively large inter-sample variation was observed from different regions of the same textile. These variations were related to spectral signal intensity, not maxima and minima wavelengths or minute shoulder bands. Other factors, such as variations in fiber thickness and light scattering inside the fiber, can affect this phenomenon. On the other hand, Wash-Gubala proposed a kinetic model to study the washing process to change the color of fabric, predict fabric color change, and treat fibers with detergent solutions. Acrylic and polyester fibers show similar changes in transmittance. Several factors influence color change, such as dye type, textile composition, type of detergent solution, exposure time, temperature, and cycle wash conditions. Many factors can alter the spectrum relative to pure dyes, such as the presence of shedding colors. They are added to the dye bath during dyeing to obtain a specific color Thus, the use of additives during the dyeing process causes deviations with respect to the patterns of pure dyes. Additives differ depending on the dyeing process.
Textile damage analysis
Textile damage analysis is an invaluable tool in forensic investigations and can be used to help solve stabbing, shooting, and sexual assault cases. It also has the potential to solve arson and acid attacks. Here, the literature is explored to review studies related to blunt force damage, stab and slash cuts, the incidence of false positive evidence in sexual assault, projectile injuries, and effects of decomposition on textile injuries, etc. It is clear that there is a dearth of research in this area, but where research has been done, it has been informative and influential. However, there are areas where more work is needed, including a better understanding of normal wear and tear and the potential for chemical damage to textiles. One area that is in significant need of further work is the development of a robust explanatory framework.
Forensic textile damage
Forensic textile damage is a specialized area of forensic science and is where fabric and textile damage is analyzed to provide information to forensic investigations. It has been used in stabbing cases where damage can be checked to determine which implements and operations caused such damage. In such cases, clothing damage can be thought of as a two-dimensional version of a three-dimensional wound. Although a wound can provide more information, it is not always available, due to medical intervention or where the deceased has decomposed. In such cases, clothing can then be analyzed. This discipline can also be used in cases of sexual assault, where clothing is applied with a blunt force and the clothing or underwear is pulled with some force, the complainant also insists by pulling on the clothing. There are also attempts to understand the impact of projectiles that damage clothing, not just bullets, but also air pellets, arrows, and crossbow bolts. More recently, with an increasing number of high-profile acid attacks occurring where corrosive substances are thrown at people and items, attempts are being made to identify chemical damage to clothing in an attempt to provide some evidence linking the suspect to the corrosive substance. As a result, the field of forensic textile damage is a specialty that is currently of great use in the advancement of criminal investigations and may become even more useful with further research.
Blunt force damage
Blunt force damages are typically characterized by tearing and punching and are usually a catch-all phrase for injuries not caused by a sharp application. This occurs when textiles or clothing are put under strain, for example, squeezed and pulled, until the fabric tears. This type of tear primarily occurs at the weakest part of the garment, which is usually the seam. Blunt force impacts (BFI), such as punches or forceful contact with an object, can also cause damage to textiles, such as distortion or expansion of warp and weft.
Sharp force damage
Sharp force damage, often called a stab wound, is where a sharp implement penetrates a piece of fabric, leaving a hole that reflects the cutting implement itself. For example, a single-edged blade will leave a different shape of cut than a double-edged blade. A blade with a serrated edge will leave a differently-shaped hole.
Projectiles damage
Projectile damage is damage caused by an object that is projected through the air and usually seeks to enter the body. The most obvious example is a bullet discharged from a firearm, but it also includes air pellets, arrows, and crossbow bolts.
Damage in sexual assault cases
Damages in sexual assault cases are blunt force harms, where clothing and underwear are forcibly removed, that is often with the complainant struggling to keep the clothes on. This can result in highly dynamic and complex damage patterns to the garment. Although by no means certain, the presence of significant clothing damage may be evidence of the absence of consent in cases of sexual assault.
Decomposition
A study of this nature is vital to understanding the effects of decomposition on textiles, as it requires an understanding of how textiles change over time under natural conditions, something that has been well explored by Beaver.
Thermal and chemical damage
One of the main causes of textile damage is useful evidence that most crimes are committed by people wearing clothes, so if someone commits an arson or acid attack, clothing is likely. Either there is thermal damage from lighting the fire, for example holding a Molotov cocktail too close to the fire sleeve, or chemical damage from splashing corrosive substances on the perpetrator. Acid attacks are becoming more and more high profile and thus, there is a need to understand the impact such corrosive substances can have on clothing. At present, there appears to be no published work on the effects of corrosive substances on textiles.
References
1. Farah, S., Tsach, T., Bentolila, A., and Dofmb, A.J. (2014) Morp Grieve hological, spectral and chromatography analysis and forensic comparison of PET fibers.
2. Zieba-Palus, J. and Was-Gubala, J. (2011) An investigation into the use of micro-Raman spectroscopy for the analysis of car paints and single textile fibres.
3. Cho, L. (2007) Identification of textile fiber by Raman microspectroscopy.
4. Thomas, J., Buzzini, P., Massonnet, G., Reedy B., and Roux, C. (2005) Raman spectroscopy and the forensic analysis of black/grey.
5.https://www.dovepress.com/forensic-textile-damage-analysis-recent-advances-peer-reviewed-fulltext-article
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