Drug traces that enter the follicles are structurally and chemically stable for a long period of time, this means that they cannot be washed, flushed or bleached out of the hair’s structure.
When cocaine, opiates, methamphetamine and PCP are ingested into the body, they are rapidly excreted and virtually undetectable in urine within 72 hours of use. The drug testing using a hair sample covers a period of months ensuring that the user cannot evade the test by abstaining drug usage for a short period. Similarly to this, certain drugs taken for therapeutic reasons can be viewed. If the subject stops taking the medication, it will show up in hair fibres.
Hair testing can also differentiate between first time drug users, recreational users and addicts, first time users will have a relatively small amount of trace substances in their hair close to the root. Frequent users will have areas in their hair which correlate to periods where no drugs have been ingested; addicts will have high levels of trace substances consistent through out their hair.
Hair testing does have some negative associations, as false positives may occur. This means that a drug free sample may be falsely reported as showing positive for certain drugs. Poppy seeds which may have been ingested on bread contain trace amounts of morphine; this can lead to a false positive for various opiates. Codeine, which is found in many pain relievers, may produce a false positive for morphine and heroin. Newly produced antibiotics including amoxicillin and ampicillin can produce a false negative for cocaine.
The forensic value of hair samples
Hair is an example of trace evidence which may be discovered at a crime scene. Hair samples are generally investigated to assist in the identification of persons present at a crime scene; hair samples are a form of associative evidence. Hair examinations using light microscopy are used to differentiate between animal and human hairs. All hair samples are different, ethnic origin can be determined from a sample, pigmentation granules, cross sectional shape, and texture are viewed to distinguish between ethnic origins. It is also possible to decipher the somatic origin of a hair sample, eyelash, pubic, auxiliary, and limb hairs show different qualities and characteristics from each other.
If the hair sample was forcibly removed from a subject, the bulb of the hair may still be present; this occurs commonly in murder and rape cases where either the victim or the attacker may have left trace samples. From the bulb, individual cells may be present allowing for the extraction of DNA, this is a unique identifier as each individuals DNA is genetically dissimilar, and this can determine if a subject was present at a particular scene.
It is sometimes possible to determine if a hair came from a child, children’s hair is usually finer and fairer than adult hair. The average human loses approximately 100 hairs per day without being consciously aware of it; this is why a hair sample is a good form of trace evidence.
Hair samples are not concrete evidence that a subject was at a crime scene, sometimes it is difficult to determine the origin of a hair sample. Hair can show great morphological differences, even when taken from the same individual. A hair sample may have been shed at a scene for a relatively long time before an offence is committed. This then places an individual at a crime scene before it is one.
Trace evidence in the form of hair samples are only presented in court when other examples of evidence are available, a conviction cannot be made on the sole evidence of a hair sample. Hair samples can place an individual at a scene but not prove when they were present.
Calibration of Microscopes
If accurate measurements are to be made using a light microscope, the eyepiece micrometer must be calibrated for each objective lens. The micrometer is calibrated by comparing the ocular scale for calibration with a stage micrometer slide, which has a known dimension. The two scales are finely focused and aligned together. The size of each ocular division is determined by comparing this with the length of the stage micrometer. This method should be repeated for each objective lens.
Calibrating Microscope #4
X40 Magnification
28epu = 1smu
1epu = 1/28 = 0.035mm
0.035 x 1000 = 35.7μm
X100 Magnification
70epu = 0.1smu
1epu = 0.1/70 = 1.4X10 ˉ³mm
1.4X10 ˉ³ x 1000 = 14μm
X400 Magnification
29epu = 0.1smu
1epu = 0.1/29 = 3.4X10 ˉ³mm
3.4X10 ˉ³ x 1000 = 3.4μm
After calibrating microscope #4, it was used for each hair and fibre sample to give accurate measurements of diameter.
Experiment
Aims
The aim of this experiment was to determine the origin of a suspect hair sample by comparing it with other control hair samples.
Equipment
Lamp
Light Microscope
Biceps
Glass slide
Cover slip
Suspect hair sample
Various control samples.
Method
The light microscope #4 was calibrated before any comparisons between hair samples were completed. The light microscope was then set up ready for comparing the various samples. Each hair sample was then taken from its sample bag using a pair of biceps. The sample was then placed onto a glass slide; a cover slip was placed over the top of the glass slide to prevent any movement of the hair whilst under the microscope. The sample was then viewed under various objective lenses. The results were recorded onto microscopic compassion paper. This method was repeated for each of the hair samples.
Table of results
Evaluation
The rabbit fur viewed under the light microscope was very thin, 23.8μm in diameter. The medulla was striated; the stripes were not consistent throughout the hair and had varying widths. The hair appeared to be curved and illustrated some kinking along the shaft. The cuticle had a knotted appearance. The cat hair sample was relatively thicker at 70μm in diameter. It was again curved and had a dark brown pigmentation. Keratinized cells were clearly present; these overlapped each other like the scales of a fish, due to this the texture of the hair was quite coarse.
The human hairs in comparison were relatively thicker than the animal hairs; the pubic hair was the thickest at 112.2μm in diameter. The human samples (with the exception of the eyelash hair) were smoother than the animal hairs. The scalp hairs had cut tips which suggested that the hair had been recently trimmed. The tips of the animal hairs were frayed or broken. Only one of the human hairs had the bulb attached; this suggests that this sample was forcibly removed. There were various differences in the shapes of the human hairs. The head sample was long and straight, where as the beard hair was short and had a triangular tip.
Determining the origin of the suspect sample
The suspect sample was short with an even diameter; it had a knotted cuticle, black pigmentation and a continuously curved shaft. These characteristics were similar to various control samples. The suspect sample however had two cut tips, both suggesting a recent hair cut. The suspect sample was 44.2μm; these traits were only common to the human scalp hair #2.
Problems with the experiment
Forensically, biceps are not used to remove hair samples from a crime scene; biceps can cause damage to the hair sample. Typically, hair is recovered by scraping, shaking, vacuuming or using tape.
The hair samples were not additionally compared under a stereoscopic microscope. A stereoscopic microscope can show details of the shape of the shaft and the pigmentation of the sample. It can clearly show if a scalp hair has been recently cut of dyed. The stereoscopic microscope however lacks the magnification power to show minute details, the medulla of a hair sample cannot be viewed with stereomicroscopy.
A forensic scientist would compare samples using a comparison microscope; it allows for the study of two objects simultaneously. Using a comparison microscope, the control sample and suspect sample may be viewed at the same time, allowing for a more detailed comparison.
Introduction to fibres
Fibres are a form of trace evidence which takes on many forms and guises. Fibres may be either natural or synthetic (man-made). Natural fibres can be sub-categorised as they may come from vegetables, animals or minerals.
Vegetable fibres may be subdivided depending upon their somatic origin, and which part of the plant the fibre comes from. Plant seeds produce such fibres as cotton, kapok and coir. The stem of various plants produce fibres like linen and hemp. Various leaves of plants produce fibres such as manila and sisal. The most common type of vegetable fibre is cotton; cotton comes from the seed hairs of the Gossypium plant. The hairs of the seed make the body of the seed light; wind catches the hairs of the seed and disperses them. Microscopically, cotton has a flat, twisted appearance.
Linen is derived from the stem of the Dicotyledonous plant. Microscopically, they are straight, long with nodes at regular intervals; they have a bamboo like structure. The main molecule which makes up vegetable fibres is cellulose.
Animal fibres may be subdivided depending upon their protein structure and composition. The main types are wool and other hair types; made up of keratin, and silk; composed of fibroin. Wool is an animal hair which comes from sheep; cashmere and mohair are goat hairs and alpaca comes from llama hair. Silks are fibres spun from the common silk worm and other insects. The fibres are spun as long filaments and have a cross-sectional shape which is triangular with rounded corners.
Mineral fibres are composed of inorganic materials and are commonly used as insulating materials as well as in the manufacture of fire resistant textiles. The occurrence of these types of materials is decreasing as mineral fibres are potentially dangerous to human health. Mineral fibres include asbestos and fibre glass.
Synthetic fibres may also be sub-categorized into natural polymer fibres and which are either regenerated or derived and synthetic polymer fibres. Microscopically, synthetic fibres have no internal structure; they are straight and have small black particles of delustrant (titanium oxide) attached randomly along their lengths. Regenerated fibres are made of natural polymers and materials including cellulose and cotton. They are produced by dissolving wood or cotton in a solvent. The solution is then forced trough a small orifice to produce a fibre. Derived fibres are produced from chemically modified polymers, generally cellulose. Microscopically, derived fibres have an irregular cross section with striation along its shaft. Derived fibres include acetate and triacetate. Synthetic polymer fibres are entirely chemically synthesised polymers; they include nylon, polyester and acrylic.
Fibre evidence provides a corroborative aid when investigating a number of cases. In an assault case, direct contact between the suspect and the victim occurs, resulting in the exchange of clothing fibres. In burglary cases, the suspect may leave clothing fibres at the point of entry, snags of fibre may also be found on broken glass and rough surfaces like brick walls.
The most common method of fibre collection at a crime scene is the adhesive tape technique; adhesive tape is applied to an area where fibres are to be obtained. When the tape is removed the fibres adhere to the sticky surface of the tape.
Forensic investigation of fibres
There are many different methods for the analysis, identification and comparison of textile fibres. The methods used by modern forensic scientists are normally none destructive, due to the fact that the fibre may require analysing more than once or the fibre even become an exhibit to be presented in court. Older techniques such as solubility testing, melting point analysis and flame testing were forms of analysis which were destructive. There are many methods for the identification of various fibre types; these range from light microscopy to more complicated methods like thin layer chromatography.
Light microscopy is the simplest method used in fibre comparisons, natural fibres can be seen and speedily compared and identified. Synthetic fibres however may not easily be identified by microscopy alone and may need other methods of identification. Nylon, acrylic and polyester may be identified using polarized light microscopy. Some fibre types may be dyed, chemical analysis such as high performance liquid chromatography can aid in distinguishing the identity of the dye.
Experiment
Aims
The aim of this experiment was to microscopically view various fibre samples to see similarities and differences between fibre types.
Equipment
Lamp
Light Microscope
Biceps
Glass slide
Cover slip
Various fibre samples
Method
Light microscope #4 was again used in this experiment as it had been previously calibrated. The light microscope was then set up ready for comparing the various fibre samples. Each fibre sample was then taken from its sample bag using a pair of biceps. The sample was then placed onto a glass slide; a cover slip was placed over the top of the glass slide to prevent any movement of the fibre whilst being viewed. The sample was then viewed under the various objective lenses available. The results were then recorded onto microscopic compassion paper. This method was repeated for each of the fibre samples.
Table of results
Evaluation
The polyester samples (1 and 7) showed some very similar traits, they were both long rope formations, sample 1 was twisted with a straight length, sample 7 showed a tightly twisted length, they both had a rounded cross section. Both samples had been dyed. They were also the exact same size of 266μm. The nylon samples also possessed similarities; all were white, single stranded and relatively thin ranging between 7 and 56μm thick. The two Polycotton fibres were white, tightly twisted rope formations; they had an even diameter along their shafts. Both Polycotton fibres were of a similar diameter.
Unknown sample 6 had similar traits to nylon as it was very short and thin at 7μm; the other two unknown samples (3 and 10) had similar traits to all of the other fibres. Methods other than white light microscopy should have been used to determine their identity.
Problems with the experiment
Similarly to the hair comparison experiment, biceps were used to remove fibre samples from their bags; this again may cause damage or distortion to the sample.
In order to make a more detailed analysis of the fibre samples a comparison microscope should be used, however due to the lack of equipment a comparison microscope could not be used.
Only white light microscopes were used, forensically polarized light microscopes are used to observe and compare synthetic fibres.
Only one example of a natural fibre was available and so could not be compared to other natural fibres.
Bibliography
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Jackson A.R and Jackson J.M, Forensic science, Pearson Education, 2007, 2nd edition
Dr. Erzinçlioglu Z, Forensics True crime scene investigations, SevenOaks publishing, 2004
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Dr. Erzinçlioglu Z, Forensics Crime scene investigations, from murder to global terrorism, Carlton Books Limited, 2006
Bruce L. Berg, Criminal Investigation (4th Ed), McGraw-Hill companies, 2007
Bell. S, PH.D, The facts on file dictionary of Forensic Science, Checkmark Books, 2004
Langford. A, et.al, Practical skill in forensic science, Pearson Education, 2005
