How hair and fibre aid in the investigation of crime.

How hair and fibres aid in the investigation of crime

Locard’s exchange principle ‘every contact leaves a trace’. Most of the forensic science revolves around this principle - it states that with every contact between two items, there will always be an exchange. This famous quote was used since the beginning of the twentieth century and basing on this theory, many crimes were able to be solved.1 Trace evidence, which the principle refers to, could be from crime scenes or accident scenes as a form of recoverable materials, marks or impressions. Although trace evidence on its own may sometimes not be enough to solve the crime, it could support other evidence or even pressurize a suspect to confess.2 This essay focuses on recoverable trace evidence such as hair and fibres and how they are analysed in the investigation of crimes.

Textile fibres as trace evidence

The term fibre is used to describe ‘any solid object that is thin, flexible and elongate, having a high length to transverse cross section area ratio’ .3 Fibres are the basic units in fabrics and they are classified into two classes: synthetic and natural. Natural fibres originate from plants and animals. Plant fibres used in the production of texile materials include flax (linen), ramie, sisal, jute, hemp, kapok, and coir. Animal fibers such as wool, cashmere and mohair are commonly found as well. Synthetic fabrics include nylon and polyester , which can be identified more easily as the cross section of the fibre may be manufacture specific.5 In the past, fabrics were used to be made with pure natural fibres until the manufacturers mixed and matched the natural and man made fibres to create variety of different fabrics. This made the identification of the fibres more difficult; however, figure 1 Top: cotton, bottom: wool 4

properties (such as how they are woven) and laboratory tests enable one to differentiate between them. Figure 1 shows a microscopic view of a transverse section of cotton (top) and wool (bottom). The diagrams show clearly the different structures and appearances between these two fibre types. Wool appears to be rougher on the walls and has a circular transverse section. Cotton has a smoother side with a curved transverse. On the other hand, the cross section of a man made fibre may be manufacturing specific and some shapes are only produced for a short period of time.6

When natural and synthetic fibres are compared, it is with much difficulty to analyse man-made fibres because (despite it could be manufacture specific) most of them have smooth surfaces. So unlike natural fibres, they cannot be analysed just by looking under the microscope- further tests would have to be performed (discussed later).

Transfer of fibre

According the Locard’s exchange principle, when there is physical contact between two fibre materials, transfer from one to another would occur. A given fibres may be transferred more than once, however, the amount of fibres transferred, depends on the duration of contact (between suspect and the victim or crime scene) and the nature of the fibres. Fibres are made in several ways as some are woven, knitted or spun to form yarn. Tightly woven fabric shed less often than loosely woven. The age of fabric also contribute to the degree of transfer: new fabrics tend to shed more readily than old. And damaged fabrics during physical contact increase the likelihood of fibre transfer.6,4

Forensic scientists would search for these transferred fibres from the scene and on victims and suspects: the more number of fibres found (and matched), the more likely that there was physical contact between victim and suspect or suspect and crime scene.7

Collection and analysis of textile fibres

When fibres are collected at a crime scene, hand retrieval and tape lifting technique would usually be followed to remove the evidence which could be found as a transferred material or may be loosely attached to objects at the crime scene. For surfaces that are difficult to tape lift, would require a vacuum.9 Collections of the fibres are done with extreme care as cross contamination from different objects would destroy the credibility of the evidence. At the laboratory, the tape would be analysed under the microscope in search of similar colour, texture and structure as the fabric of the supposed source. Colour comparisons of found fibres to the original source are done using a micro spectrophotometer which can produce an absorption spectrum and view the fibre under the microscope at the same time. Infrared spectrometers are also used in fibre analysis as the obtained spectrum can tell the chemical composition of the material. Figure 2 shows the IR spectra of acylic fibre and cotton. IR spectrum for natural fibres would result in braoder peaks compared to synthetic fibres. As shown in the figure 2b, cotton has a larger and broader stretch.

A more traditional method would be using thin layer chromatography to separate the dye (which is first extracted using solvents) into its components.10

As mentioned previously, man made fibres are more complicated to analyse: they are constructed in such a way that it is thicker in the centre and thinner on the walls. This property is caused by the alignment of molecules in the polymer with the length of the fibre during the

manufacturing process. Due to this figure 2a (top) acylic fibre, 2b (bottom) wool 15

characteristic, refractive indices are found in synthetic ...

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A more traditional method would be using thin layer chromatography to separate the dye (which is first extracted using solvents) into its components.10

manufacturing process. Due to this figure 2a (top) acylic fibre, 2b (bottom) wool 15

characteristic, refractive indices are found in synthetic materials. The fibres are placed in a fluid containing a comparable refractive index, and the disappearance of the Becke line would occur under a polarising microscope. This technique can determine whether the fabric was torn or deliberately cut and can show the ‘freshness’ of damage.10

Case study of Kristen Harrison

A case where the colour analysis of synthetic fibre played an important part in connecting two crimes, was seen in 1982, when Kristen Lea Harrison was abducted in Ohio and her body was found six days later- strangled and raped. Distinctive orange fibres were found in her hair which looked like the ones found on a 12 year old murdered female, eight months ago. The evidence was concluded to be carpet fibres due to the odd shape and was analysed to be polyester.

Some days later, another woman was abducted but was able to escape. She reported to the police who took action in immediately in finding the suspect. It was discovered that the orange carpet from the suspect’s van matched the fibres found on the victim’s hair. Due to the unique colour of the fibres, forensic scientists were able to find the manufacturer- apparently only 74 yards of carpeting were shipped to Ohio. This finding made the fibre evidence more narrowing, and it backed-up other evidence in convicting Robert Anthony Buell.11

The origin, the colour as well as the number and location of the recovered fibres are very important in relating the evidence to the crime. The amount of fibres found at a crime scene or on suspects or victims indicate the nature of contact: in violent attacks, more fibres would be transferred onto the victim. Trace evidence can be primarily transferred (direct transfer from one object to another) or via an intermediary object- secondary transfer. Determining the location of the recovered fibres, allows one to relate the involved people to the scene of crime and it also adds to the value of association when found on different areas of the body.5

Case study of Wayne Bertram

The value of fibre association can be seen in the conviction of Wayne Bertram Williams, in which fibre evidence played a significant role. Between the summers of 1979 and 1981 in Atlanta, Georgia, USA, Williams was linked to the murder of two men found in the River as well as the murder of 10 young males and the disappearance of another 18 young Africa American males.

The last known victim, Nathaniel Cater, was found in the Chattahoochee River on 24 May 1981. The medical examiner determined the death as caused by ‘probable asphyxia’. However, he was unable to determine exactly when and how the death occurred. The examiner stated that ‘Cater had been dead just long enough for Wayne Williams to have thrown him off the bridge several days earlier.’ 12 Two days before the body discovery, Police officers heard a loud splash from the river and directly above they saw Wayne Williams’s car on the bridge. Williams was pulled over for questioning and gave false details about where he had been. The police officers were very suspicious of him, and when Cater’s body was found- they believed Williams was connected to the case as well as 10 other murders of young males.

Through the string of murders he was involved, a large amount of fibres were found on the victims. The FBI was interested in matching the evidence to Williams. A search warrant was granted for Wayne Williams’ house and vehicle, it was discovered that the fibre evidence found on Cater matched the samples in Williams home (on bed sheet, carpet, blanket and a dog). Further 28 fibre types were found on 19 different items of William’s residence and car. This linked him to the murder of other victims. Wayne Williams was sentenced to two consecutive life sentences for the murder of Nathaniel Cater and Jimmy Ray Payne.13

From this case, using textile fibres as evidence, the association of several murders was able to be linked together. The fibres evidence also indicated the nature of contacts between the involved people and this allowed a crime scene reconstruction.

Hair as trace evidence

Another type of trace evidence to be discussed is hair which is defined as ‘a fibre that grows out of a hair follicle in the skin of mammal’.14 The study of hair is known as trichology which is widely performed now days to analyse a person’s health or to testify the use of illegal drugs. However, the importance of trichology is not only used in the medical aspect, but also in the forensic world. Hair is a good source of trace evidence in crime solving because unlike textile fibres, it sometimes may contain DNA to identify suspects or at least give information about the suspect, such as the race.

Structure of hair

The morphology of hair varies from species to species, however the basic structure remains the same. Hair contains three main features: cuticle, cortex and the medulla. Cuticle is the most outer layer, followed by the cortex which makes up majority of the hair mass. The most inner layer is the medulla which extends through the hair. The length and shape of the hair can show where from the body it originated. The human hair is classified into six types, namely, head hair, pubic hair, eye brow and eyelashes, beard and moustache and under-arm hair. This is especially important when identifying the type of crime committed, for example, to determine whether there was sexual assault involved at a murder scene.

Distinction between human and non-human hair

In forensics, the fundamental distinction between human and non human hair has to be made first before further analysis. In the human hair, the medulla and cortex contain pigments which are generally distributed on the outer part of the cortex and a non human hair contains pigments that are more centralised. The appearances of the medulla are different in human and animals: it is narrower in the human hair compared to the animals’ which makes up more than half the diameter of the hair. Another difference would be that there is less scale pattern along the length of the shaft in human. Whereas the non human hair would contain more scale patterns. The human medulla, with the exception of Mongoloid race, is fragmented. Animals have a continuous or discontinuous medulla. Basing on these known differences, forensic scientists are able to determine whether the found hair is of human or animal origin.16

Identification of human hair

Indication of racial type can be deduced from looking at the morphology of hair. Hair examiners categorise hair into 3 groups: Africa, European and Asian. A pure African race has curly hair with an oval cross section (fig 3b). Their pigment granules are larger than the other two racial groups. A European ancestry has hair that

is either straight or wavy. The cross section of the hair would be circular or oval and the pigments in the medulla would be evenly distributed. Asians have hair that is straight with a circular cross section (fig 3a). The pigment granules are grouped together. Despite the three main racial categories, it is difficult to identify people from a mixed race as their morphology would differ from the ancestries.

Sex and the genetic profile can also be identified from hair; however the root has to be present. The cells at the tip of the root contain DNA which can be extracted. In growing hair, there is more DNA material than hairs from telogen (resting) phase.19 figure 3a (top):cross section of Asian hair17

Figure 3b(mid)cross section of African hair17

figure 3c(bottom)SEM of European hair17 Sometimes, naturally fallen hair may not contain enough DNA to perform analysis, but it might contain mitochondrial DNA. Forcibly removed hair can usually undergo DNA analysis as pieces of tissues may be attached.15

From the identification of human hair, forensic scientists can deduce the race, sex and sometimes the personal identification of the suspects. Hair as evidence can also reconstruct crime scenes and determine what type of violence was involved. Testifying the present of drugs or poisons in the hair can too determine the nature of deaths.

Collection and analysis of hairs

Hair fibres are collected in the same manner as textile fibres from crime scenes (such as the use of sticky tape, vacuum); however tweezers are not recommended as it may destroy the structure of the hair. Shaking and brushing from clothing materials are commonly used to obtain evidence. When analysing hair, microscopy and DNA analysis are the main techniques of identifying the origin of hair: Scalp hairs tend to show little diameter variation; pubic hairs are short and curly with wide variation in the shaft diameter and beard hairs are course with blunt tips.15 Ultra-light and visible microscopes are also common tools as they are capable of producing high magnification. Mounting the fibre in a medium allows light to penetrate through the hair fibre-letting internal structures to be viewed.14

Textile fibres and hairs as evidence

Textile fibres and hairs interlink in crime scenes: they are often collected and examined in the same manner. Transference of this type of trace evidence is the same, except fibres are more easily transferred. The two recoverable materials as evidence can be seen in the case of Sarah Payne.

In July 2000, eight year old Sarah was abducted in Sussex whilst playing with her siblings. Her body was found seventeen days later, decomposed. Police officers were able to find the suspect, Roy Whiting, very soon as he was a known paedophile in the area. He had a van which was taken for forensic examination and all contents were removed from the vehicle, which included a red sweatshirt, socks, a checked shirt and a clown patterned curtain. A shoe of Sarah’s was previously found close to where her body was discovered. It was examined to contain fibres from her school clothes as well as fibres matching the red sweatshirt from the van. This was the first evidence linking Sarah to the van.20

Sample evidence from Sarah’s dress worn on the day of disappearance, was taken from her friend’s dress of the same make (but different in colour). Forensic analysis was able to determine the structure of the fibre from the dress and use it as a control fibre. This control fibre was used when comparing fibres from the red sweatshirt.

The red sweatshirt also contained a single blonde hair fibre and DNA testing proved that it was the victim’s hair.

However, during the trial, it was argued that there was cross-contamination when storing the evidence. The defence side stated that this was the reason for finding Sarah Payne’s hair on the suspect’s red sweatshirt. On the other hand, an FSS scientist told the jury that cross contamination in the manner suggested from the defence side, was very unlikely.21

In December of 2001, Roy Whiting was found guilty and sentenced to life imprisonment.

From this case study, it can be learnt not only the value of textile and hair fibre as evidence, but also the importance of collecting and storing them in a proper manner. Cross contamination of fibres loses the credibility of the evidence- forensic scientists and crime scene officers would need to handle them with extreme care.

Textile fibres and hair fibres, like most other recoverable evidence, can tell a story of what happened at a crime scene. Basing on Locard’s exchange principle, the fibres have a great tendency of transferring onto another object. Due to this property that they possess, it is to the crime solver’s great advantage to link suspects to a particular crime and reconstruct it. Analysis of fibres morphology indicates the origin of it and the nature of contact involved. Hair tells the sex, race and sometimes the person’s identity. Using the information that these types of trace evidence provide, crimes can be successfully solved.

References:

Lotter, K.(2008). Locard’s Exchange Principle[online]. Available from: [accessed on 13 March 2010]

enotes. (2010). Locard’s Exchange Principle [online]. Available from: [accessed on 13 March 2010]

Jackson,A.R.W & Jackson, J.M. (2008). Forensic Science. 2nd edition. England: Pearson education limited. p49

Unofficial NSW police. Forensic Scientists hair and fibres [online] available from: [accessed on 13 March 2010]

Deedrick, D.W (2000). Hair, Fibres, Crime and Evidence. [Online]. Available from: [accessed on 19 March 2010]

Houck, Max M.(2001) Mute Witnesses Trace Evidence analysis. London: Academic Press.p15

Houck, Max M.(2001) Mute Witnesses Trace Evidence analysis. London: Academic Press.p16

Robertson, J &Grieve, M(eds).(1999).Forensic Examination of Fibres.2nd edition. London: Taylor &Francis Ltd. P103

Univeristy of Hull. Fibre Analysis. [online] Available from: [accessed on 15 March]

Bell, R & Bardsley M. (2010) The Atlantic Child Murders-fibre analysis. [online] Available from: [accessed on 6 April 2010]

Bell, R & Bardsley, M. (2010) The Atlantic Child Murders- Building the case. [online] Available from: [accesed on 6 April 2010]

Manning, J (2000). The Atlanta Murders. [online] Available from: [accessed 6 April 2010]

Jackson,A.R.W & Jackson, J.M. (2008). Forensic Science. 2nd edition. England: Pearson education limited. P57

Chaloner ,P. (2009). Forensic Analysis,F1070, [lecture notes]. Trace and Contact Evidence 1. Introduction to forensic chemistry. University of Sussex, Chemistry department, Sussex, 6 November.

Enots. (2010) Hair Analysis.[online]. Available from: [accessed on 13 March]

Wei, X. (2006) What is Human hair? A light and Scanning Electron Microscopy Study.[online] Available from: http://www.optics.rochester.edu/workgroups/cml/opt307/spr06/xue/project.htm [accessed on 8 May 2010]