Forensic fabric analysis in criminal investigations

Forensic Fabric Analysis

Some of the basic tools that a fabric examiner should at least have at any given moment include a stereomicroscope, along with a composite light microscope that is fitted with polarized light capability, and a comparison microscope. When examining both questioned and known fabric, the examiner must do this side by side, and within the same magnifications in terms of visible light. Alternative lighting, which includes fluorescent lighting and polarized light, is not necessary but when the equipment used allows, is highly recommended. In certain types of analyses, such as when testing for solubility, you may need to examine the questioned and known fabric near each other, and on one slide, or in the spot plate's wells that are adjacent to each other. However, you need to exercise extreme caution where loose fabric is concerned not unless you have no problem with identifying the source of each fabric (Innes, 2000).

Fabric examination is a process that often involves comparing different samples from the known and questioned sources in order to verify if they share certain characteristics. This would then indicate that they are from a single source (and an example of this is the carpet that is obtained from the car used by a suspect compared to foreign fabric that has been found on the victim's clothing). Such comparison includes recognizing and evaluating the class characteristics that link any material to a group without tying it to a single source. On the other hand, certain individual characteristics also display that there is a linkage amid two or maybe more items with one another, while excluding all the other items. Fabric examiners would come across such a scenario where physical matching is required for pieces of fabric or cordage (Innes, 2000).

Identification of Source

Exchanging of textile fabric between individuals, or between individuals and objects, or between objects alone, is possible. Any fabric that is linked with an identifiable source, which may include fabric that is obtained from a suspect, victim, or scene, the examiner has to place a value on such an association. Such a value has a significant weight, which depends on a variety of factors that range from type or types of fabric found, the color or colors of fabric, the numbers of fabric, the location or locations of the fabric, in addition to the multiple linkages between the fabric. The nature of contact as well as the transfer and persistence of the fabric are the other factors that determine significant weight (Lyle, 2004)

Whenever a fabric is transferredor detected, this often depends on the nature and amount of time that elapsed when the suspect and victim came in contact, in addition to the fabric's persistence once the transfer has taken place (Lyle, 2004).

Types of Fabric: How rare or common the type of fabric found at the scene of crime or on the victim or suspect is, often affects its probative weight. In textile production, no other type of plant fabric is as commonly used as cotton fabric. Cotton fabric is often quite diverse, and this hinges on the type of cotton, in addition to the length of the fabric, and the amount of twist. The value of cotton fabric identification is also dependent on processing techniques and color applications. The significance of the plant fabric is influenced or enhanced by the presence of other less common varieties that are found at the scene of crime and on the clothing found on the victim or suspect.

Colors of Fabrics: Color is often the greatest variety seen in textiles. When talking about fabric comparison, nothing comes close to its color. Synthetic dyes as well as pigments form part of 29 various chemical categories that boast of more than 12 different methods of application (7). Converting the raw materials into a refined dye, would often require between eight and ten processes. The annual production of a specific dye is often not more than 10 tons, and within the dyeing industry small batches are increasing in popularity, with colors of fabric being one of the most powerful discriminants. The significance of color is seen when the whole spectrum of colors is spread out on a wide variety of garments and carpeting that is produced in a given year, especially when multiplied with the amount of garments and carpets that were produced in all the previous years (Lyle, 2000)

Quantity of Fabrics: When determining the actual contact, one has to look at the number of fabric that was identified on the victim's clothing, and find out how it compares with clothing found on the suspect. Where the number of fabric is higher, the chances of there being direct contact between the suspect and victim are equally high. On the other hand, the opposite of this does not have to be true all the time, even where a single fabric association has both probative and scientific value. Even when you do not find any fabric, this does not mean that there was no contact between the suspect and the victim. Each case should always be treated on its merit, and the examiner is required to weigh all the relevant factors before coming to any conclusion regarding the worth of each evidence (Saferstein, 2004).

Fabric Position: The probative eight or value of the fabric in question often depends on where it is found. The significance of the fabric association also depends on its location on the body or on particular items (Saferstein, 2004).

Fabric Sort: The construction of any fabric, also affects the number and types that may be transferred between the suspect and the victim. Tightly woven and knitted fabric never shed as much fabric as those that are loosely knit or woven. Similarly, filament yarn fabric does not shed as much as the fabric that is made of spun yarns. Some specific fabrics also transfer readily compared to others. The amount of fabric transfer depends on the condition and wear of the same. In newer fabrics, you will see too much loose fabric located on its surface, while worn fabrics are full of damaged areas where fabric easily sheds. During physical contact, a damaged fabric will often experience more transfer (Saferstein, 2004).

Multiple fabric Associations: If there is a close link between fabric types found on the suspect, victim, and the scene, this increases the chances that there was contact. Every associated transfer of fabric is looked at independently, and where multiple associations are visible, this indicates that the presence of fabric is a coincidence (Saferstein, 2004).

Type of Contact: If a fabric examiner wants to determine the number of fabric that was transferred, then a look at the physical contact between the suspect and victim should be evaluated. Where you find numerous fabric transfers, this is often indicative of the fact that violent physical contact took place (Bartos, 2012).

Fabric Transfer and Persistence: The method under which the transfer of textile fabric to the surface is possible directly or indirectly, identified as primary and secondary respectively. The possibility of transfer depends on the types of fabric that is involved during the contact, as well as both the nature and duration of the contact that took place between victim and suspect. Studies indicate that transferred fabric often gets lost at a geometric rate, and that this depends on the types of fabric that is involved as well as the movement of the clothing after establishing contact. For example, the clothing on a homicide victim could retain some transferred fabric for a much longer time simple because of the victim's lack of movement. The immediate retrieval of clothing is important and investigators should not hesitate with this, although it may be difficult to tell accurately how much fabric remains on the clothing items found on a living individual (Bartos, 2012).

Fabric Evidence

Fabric is similar to hair in that it is amazing evidence used in tracing because it sheds easily, and sticks to skin as well as garments. Fabric is also similar to hair in that it is easily transferred between people, the scene of crime, cars, clothing, home, cars and more. The objective of most investigators is to trace and identify the source of a fabric as well as its manufacturer once they come across it at the scene of crime. All fabric is grouped into three main groups (Lyle, 2004).

Natural: This is derived from animals, plants, and minerals. Microscopic examination is used to identify this type of fabric and make comparison with others (Lyle, 2004).

Manufactured or Man Made: This is made from cotton or wood pulp derivatives, and forms after being dissolved and cellulose extracted. Afterwards, cellulose is regenerated to form fabric (Lyle, 2004).

Synthetic: This type of fabric is from polymers, which are made from single molecules, after which they are strung together thus forming larger molecules. Examples of synthetic fiber include nylon and polyester (Lyle, 2004)

When examining fabric, the first process is to do this under a stereomicroscope, where you evaluate the shape, color, and size in-depth, and look for the presence of other debris. Afterwards, use a comparison microscope to compare two fabric side-by-side. The following tools will help you in finding the physical and chemical traits of a fabric (Lyle, 2004).

Birefringence: Whenever light is passed through synthetic fabric, it has to be refracted twice if it is to emerge as two completely different wavelengths of polarized light, where each type has its own refractive traits." (Lyles, 2004). After you birefringence two fabrics, you can then compare them and identify.

Microspectrophotometry: You can use this to determine a fabric's true color with the highest form of accuracy (Lyle, 2004).

Polarized Light: Here, determining reflective index is possible, and this contributes in establishing the fabrics makeup (Lyle, 2004).

Refractive Index: Direct a narrow light at a fabric before calculating the extent at which light bends and passes through (Lyle, 2004).

Scanning Electron Microscope (SEM): This is predominantly used when fabric is damaged. Uncovering subtle details on the fabric's structure and exposing the extent on damage that took place is carried out here too (Lyle, 2004).

SEM is often used in combination with dispersive X-Ray Spectrometer. Similarly, the other procedure employed here involves the use of Gas Chromatography with Mass Spectrometry (GS/MS) which produces chemical composition that is separate and helps with identification of the fabric's chemicals in addition to pigments, which are added before and after the manufacturing procedure. With these two procedures, identifying manufacturer and the source of the fabric is possible (Lyle, 2004).

Collecting and preserving fabric evidence:

Handling fabric is important and should be carried out in the same manner that is used with hair, and must involve scrupulous care if you are to prevent potential cross contamination. If you want to remove fabric from the scene of crime, you can use tape or forceps. On the other hand, while carrying out this task, you must pay great attention to the tiniest of details if you intend to preserve the fabric without causing untold damage, or collecting what you do not need (Nickell and Fischer, 1999 ).