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Introduction
What are fibres and why are they important to forensic analysis?
Fibres are quite key to forensic analysis. Fiber evidence can be considered as an example of trace evidence. They can be directly or indirectly transferred between the suspect and the victims. They are usually found in sexual assault, murder cases, hit and run cases, , burglary and hit and run cases. (Slideshare.net, 2014)
Fibres are long strands of material, which can be either natural or manmade in origin. Natural fibres are either of plant or of animal origin and can vary in length. Manmade fibres are often cut to a specific length. Fibres are not used as such. They are often fused into yarn.
Natural fibres-
There are many derived from plants and animals, which are used in the construction of the fabric. These include cotton, wool, linen, jute, hemp, kapok etc. The most common plant fibre is cotton, while the others are less common. Cotton fibres can themselves be differentiated on the basis of their length, type of cotton and twistedness in the fibres. Wool is the most popular animal fibre with the wool from sheep being the most common, while wool from other sources like rabbit, alpaca etc are less common. Wool is distinguished as fine wool or coarse wool, depending on where it is used. (FBI, 2014)Artificial fibres are man made fibres. Some are manufactured from natural sources while others are synthetic in origin.examples include polyesters, nylons, cellulose acetates.
Fibres can be woven into textiles or fabrics. Textile Fabrics which are used to make the clothing we wear, are composed of fibres, which are often coalesced, together to form yarns. Fibres can range from 10-50 micrometer. Forensic analysts need to be aware of the composition of fabrics, besides the nature of fibres. Fabrics can be woven, knitted and non woven. Understanding the source of manufacture of the fabrics, their production style and machinery, can help them to compare fabrics. Besides which, any wear or tear on the fabrics, can be used to match with possible sources of injury including mechanical injury
Fibre Transfer and Retention
Fibre samples are collected from the scene of crime, from the clothing of victims differing fibres would indicate different sources and hence can point towards possible culprits. How can fibre analysis help in forensic science or solving a crime? During a crime or violent situation, involving physical contact between the suspects and the victims as well as suspects, victims and objects, there could be an exchange of fibres or a transfer of fibres from one to the other. Identification, Recognition and recovery of the transferred fibres could lead to Fibre matching which could lead to a value regarding the kind of association between the suspects, victims and objects in a crime scene. But whether a fibre could be detected and identified will depend of following factors:
1. How long the contact was between the suspect, victims and objects in the crime scene? The force of the contact?
2. How long the fibres adhere to the objects or the materials worn by the suspect/victims, after the transfer?
3. Nature of the fibres.
4. Condition of the garment
5. Nature of the fabric on which the fibres are transferred
Other factors which also affect the determination of an association include:
1. Shape of man-made fibres- Some of these fibres have characteristic cross sectional shapes which can be used for identification of association by way of identifying the manufacturer.
2. Color of the fibers- very important criteria for association. The intensity of color, kind of color, how it is applied and dyed are factors which can be used to do fibre matching.
3. Fibre number – greater the number of fibres, the more can it be said that contact has occurred.
4. Fibre location- where it is located.
5. Presence of cross transfers and multiple transfers of fibres increases the chances of possible contact between suspect and target. (FBI, 2014)
The more unique and rarer the fiber found, the more useful and importance would it be to forensic investigations.
Some challenges with fibre analysis are the fact that there are possibilities of contamination with other material from other sources and hence fibre analysis has to be done very carefully following strict regiment to ensure lack of contamination. Another issue is loss of fibre.
Therefore it is very important to recognise, detect and identify presence of fibres at the earliest as Transferred fibres may be transferred again, relocated or lost. Hence the identification and recovery of fibres should be done at the crime scene at the earliest, as any shift or change in position of the object or victim, may result in the transfer and thus loss of fibres which could be used for identification of suspects as well as fixing what probably occurred during the crime scene. The chance of finding transferred fibres reduces with increased time following the crime incidence
Fibre Analysis
Standard forensic examination of fiber evidence involves the following steps: (Anonymous, 2014)). Fibre testing is carried out to that extent that you get unambiguous results on the identity of the
1. Fibre Examination- in fire cases.
2. Fibre Identification- which class or sub class a fibre belongs to, can be determined by Brightfield Microscopy in conjunction with other techniques such as polarized light microscopy, solubility tests, melting point determination, natural fibre tests (staining and physical tests) and Fourier Transform Infrared Microspectroscopy (FTIR)
2.(Anonymous, 2014)
3. Fibre Comparison
Comparison of known samples and the transferred test fibres from the scene of the crime, either collected directly or indirectly. Comparison is done on the basis of similarity in stereomicroscopic experience using techniques such as bright field comparison microscopy, fluorescence comparison microscopy, microspectrophotometry (MSP) and thin layer chromatography (TLC). many kinds of details are observed and noted including size, shape, color, texture, location, what it was adhering to, number etc. Their mode of rotation of light is a key determinant of the source from which they are determined.
Fibres can be judged as belonging to the same kind, when they are indistinguishable in composition, stereomicroscopic appearance, by TLC or microspectrophotometry.(An onymous, 2014)
Fibre retention:
And hence, study of fibre retention becomes very important. All materials will not retain or lose fibers easily. The number of fibres transferred between objects and human beings depends on various factors. The factors which determine the transfer of fibers include the type of fibers involved in the contact, the kind of contact and the duration of contact. Even if the fibers are transferred between the parties/objects involved, there is no guarantee that the transferred fibres would be retained. Research has shown that In fact, following the transfer of fibers onto a recipient surface, there is an initial loss of fibres, which could be as high as 80 %. (Encyclopedia of forensic sciences, pg 117) even before the first 24 hrs of the incident. Hence it is very important that the transferred fibres be recovered and collected as earliest as possible.
It has been evidenced that the persistence of fibres or rate of retention of fibres by materials depends on the following factors:
1. How strong or impactful is the contact between the donor and recipient. Weaker the contact, more would be the loss of fibres.
2. Location of contact- persistence of fibres is more, when the area of contact is less exposed to other contacts with other surfaces.
3. Persistence is less, when recipient objects are used or worn by the user or wearer.
4. When the recipient object or attire is placed alongside other objects, persistence of fibre becomes lesser.
5. Kind of fabrics involved – retention of fibres is also dependent upon the kind of material involved. Leathery materials for e.g. show more persistence of fibres as compared to garments
There are some which can be considered to be more ideal donors or recepients than others.
Another factor which influences fiber transfer and retention is the color of the fiber. Fibre analysis studies of transfer of fibres from different coloured fabrics to cinema seats have shown that the colored fibers most commonly transferred were grey black cotton and blue cotton. All other color combinations were lesser than 5 % (http://www.ncbi.nlm.nih.gov/pubmed/11731196). Spectral analysis can also be used to identify fibres which are less commonly seen and hence of greater value for forensic evidence. And it has been shown that blue, black and red cotton fibres are amongst the most commonly seen in fibre analysis (http://www.ncbi.nlm.nih.gov/pubmed/17941327_ )
Aim:
To study the fibre retention of some fibres on selected surfaces (human and fabric)
Methodology:
In this order to understand this phenomenon, rate of persistence of several kinds of fibres on some materials were carried out using fibre decay studies. The fibres included cotton, wool, acrylic. The experimental protocol was that adopted by Palmer and Burch (2009) and Palmer and Banks (2005). The transfer of fibres from a pink colored piece of cotton material to a variety of material was studied. The recipient materials were cotton, jeans and wool material. The pink material was rubbed against the sets of different material and then fan, placed at a defined distance, was switched on for different durations of time ( 10, 20 and 30 seconds) and the number of fibres which remained on the recipient material after these intervals of time, were noted. The dates were recorded. In short three different sets of experiments was conducted along with controls in which no fibers were transferred to each of these materials. The fan was used as it would provide air or breeze which would blow the fibres away. This is used as a simulation of what happens in real life, where we can easily transfer fibres to each other as well as lose transferred fibres as a result of various reasons such as wear and tear, wet, hot and windy weather, changing your clothes, leaving your clothes on top of some objects or giving it to another person.
We will be looking at how long these fibres will stick to the fabric after this experiment.
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The variables were as follows:
1. Independent variables: time, temperature, humidit
2. Dependent variable: decay of transferred fibres
3. Controlled variables: kind of fibres, kind of surfaces
Results:
Graph showing the number of fibres retained by cotton, jeans and wool material after 10, 20 and 30 seconds treatement with fan
Number of fibers retained by Cotton Jeans Wool
|
Time |
10 20 30 |
||
|
|
15 |
12 |
9 |
|
|
20 |
15 |
10 |
|
|
40 |
30 |
24 |
Decay of the fibres which is a reflection of its persistence was similar to this image. The results showed that by 24 hours no trace of fibres was retained on the skin of the test subjects. Results also indicated that wooly material retained more fibres than other material. ( adopted from (Contact Traces, 2013)) (Palmer and Burch, 2009)
Discussion:
Fibre transfer is an important aspect of fibre analysis for forensic investigations. Fibres can be directly or indirectly in which case it is called primary or secondary transfers. The nature of its transfer, how much of its retained, how much of it is lost from the recipient, depends on many thing including the nature of the recipient and donor also as well as factors such as how prolonged the contact is, how undisturbed the recipient is. The reason why the patterns of fibres on an object or person important to crime investigators is due to the fact that it gives a probable picture of where the people would have been at some point of time immediately before the crime had occurred. And hence the earlier the fibres are obtained, the more it would help with the investigation. ((Contact Traces, 2013)
The experiments were conducted to understand how different fibres are retained by different materials. Understanding the persistence time and rate of decay of fibers, which constitute vital evidence during crime scene scenarios, will help in conducting better and improved fibre collection methods and help ensure that transferred fibres from alleged suspects or objects are retrieved at the earliest before they are lost. As it can be seen, on two different kinds of material surfaces, different kinds of persistence was observed. In our experiment, we found that wool fibre was retained the most on the different material
Research has shown that on human skin, cotton or short haired fibres were retained the most, This was in accordance with the findings
from Palmer and Banks (2005) and Palmer and Burch (2009)
Therefore, to help more accurate and effective fibre analysis, effective methods of fibre retrieval should be in place. Common methods used include “adhesive lifts, pick methods, vacuum sweepings” Adhesive methods involve using an adhesive tape to lift off the fibers from the location or object or person. Pick methods involve using tweezers or other delicate instruments for picking up fibers. Vacuum approach is to use special vacuum instruments to vacuum the surface with the potential sources of fibres which can then be used for subsequent analysis. (Anonymous, 2014)
Fibre transfer and persistence is very important to forensic research as even able to obtain critical fibers, at the earliest possible time, can make the difference between catching and punishing a criminal for his crime as is seen in this case from Australia, where the fibre analysis of fibres from the footwear of the victim helped lead to the eventual punishment of her killer (Anonymous, 2014)
List of References:
Anonymous. 2014. [online] Available at: http://www.mcscs.jus.gov.on.ca/stellent/groups/public/@mcscs/@www/@com/documents/webasset/ec082283.pdf [Accessed: 14 Mar 2014].
Anonymous. 2014. [online] Available at: http://www.crime-scene-investigator.net/Phys_Evid_Manual_OR.pdf [Accessed: 14 Mar 2014].
Anonymous. 2014. [online] Available at: (http://projects.nfstc.org/trace/docs/final/BENNETT%20Case%20Study.pdf [Accessed: 14 Mar 2014].
Anonymous. 2014. [online] Available at: http://www.swgmat.org/Forensic%20Fiber%20Examination%20Guidelines.pdf [Accessed: 14 Mar 2014].
Contact Traces. 2013. Interpretation of forensic fibre evidence - transposing the conditional. [online] Available at: http://www.contacttraces.co.uk/interpretation-of-forensic-fibre-evidence-transposing-the-conditional [Accessed: 14 Mar 2014].
FBI. 2014. Hairs, Fibers, Crime, and Evidence, Part 2, by Deedrick (Forensic Science Communications, July 2000). [online] Available at: http://www.fbi.gov/about-us/lab/forensic-science-communications/fsc/july2000/deedric1.htm/deedric3.htm [Accessed: 14 Mar 2014].
FBI. 2014. Hairs, Fibers, Crime, and Evidence, Part 2, by Deedrick (Forensic Science Communications, July 2000). [online] Available at: http://www.fbi.gov/about-us/lab/forensic-science-communications/fsc/july2000/deedric1.htm/deedric3.htm [Accessed: 14 Mar 2014].
FBI. 2014. Hairs, Fibers, Crime, and Evidence, Part 2, by Deedrick (Forensic Science Communications, July 2000). [online] Available at: http://www.fbi.gov/about-us/lab/forensic-science-communications/fsc/july2000/deedric1.htm/deedric3.htm [Accessed: 14 Mar 2014].
Nuffield Foundation. 2014. Working with Science Fibres and Fabrics. [image online] Available at: http://www.nationalstemcentre.org.uk/dl/6aed14bb55a8bba29299762f9efb5383794f2092/8090-Fibres%20and%20Fabrics.pdf [Accessed: 14 Mar 2014].
Slideshare.net. 2014. Forensic Science - 03 Fibres and fabrics. [online] Available at: http://www.slideshare.net/portlester/forensic-science-03-fibres-and-fabrics-2013 [Accessed: 14 Mar 2014].
Jackson, G., and C.N. Lowrie. "Recovery of transferred fibres." Forensic Science International July-Aug. 1991: 111-119. Academic OneFile. Web. 14 Mar. 2014.
J. Roberston, C. B. M. Kidd, and H. M. P. Parkinson, "The Persistence of Textile Fibers Transferred During Simulated Contacts," in Journal of the Forensic Science Society (1982) 22:353-360.
Robertson J, Roux C. (2000). Fibers: Transfer and Persistence. Encyclopedia of Forensic Sciences; 834-838.
Robertson J, Roux C. (2010) Trace evidence: Here today, gone tomorrow? Science and Justice; 50 (1): 18-22.
Rothe M. Examination of Foreign Fibre Populations. Proceedings of the 5th Meeting of the European Fibres Group, Berlin, Germany, 1997, p 119-120.
Roux C, Robertson J. (2000) Fibers: Significance. Encyclopedia of Forensic Sciences; 829-834.
Palmer, R., Banks, M. The secondary transfer of fibres from head hair. 2005. Science & Justice, 45(3), 123-128.
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