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CRIM 355 (15)
Chapter 10

CRIM 355 Chapter 10: Hairs and Fibres

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CRIM 355
Gail Anderson

CHAPTER 10: HAIR AND FIBERS  Transferred trace evidence can corroborate other evidence developed during the course of an investigation if recovered FORENSIC EXAMINATION OF HAIR  Hair = physical evidence  Appendage of the skin that grows out of the hair follicle  Not yet possible to individualize a human hair to any single head/body through its morphology  Presumptive evidence unless corroborated by DNA  Removal from body denotes physical contact between a victim and perpetrator -> crime of a serious/violent nature  Can provide corroborative evidence for placing an individual at a crime site  Resistance to chemical decomposition + ability to retain structural features over a long period of time [thanks to the cuticle] MORPHOLOGY OF HAIR  Length of a hair extends from its root/bulb embedded in the hair follicle, continues into the shaft, and terminates at the tip end  Shaft is composed of 3 layers + is subjected to the most intense examination  Cuticle: scale structure covering the exterior of the hair  Formed by overlapping scales that always point toward the tip end of each hair  Scale from specialized cells that have keratinized and flattened in progressing from the follicle  Scales from most animal hair can be described as looking like shingles on a roof  Variety of patterns formed by animal hair makes it an important feature for species identification  Three patterns: coronal (crown like – resembles a stack of paper clips), spinous (petal like scales – triangular and protrude from the hair shaft), imbricate (flattened scale – consists of overlapping scales with narrow margins)  Resistant to desiccation (keratinized)  Cortex: main body of the hair shaft  Made up of spindle-shaped cortical cells aligned in a regular array, parallel to the length of the hair  Major forensic importance: gives the hair distinctions and points of comparisons among different individuals  Pigment granules gives hair its colour  Structural features are examined after hair has been mounted in a liquid medium with a refractive index  Medulla: Cellular column running through the center of the hair (canal in the center)  Collection of cells that looks like a central canal running through the hair  Predominate feature  The index measures the diameter of the medulla relative to the diameter of the hair shaft (medullary index)  Humans: index is usually less than one-third  Presence and appearance vary: not all have medulla + when they do, the degree of medullation varies  4 classifications: continuous (rare), interrupted, fragmented, absent  Exceptions: Mongoloid race have hairs with continuous medullae  Humans have medullae that give a nearly cylindrical appearance Root  Root and surrounding cells provide the necessary tools to produce hair and continue the growth  The shape and size of the root is determined by the growth phase  Anagen phase: initial growth phase during which hair follicle actively produces hair (may last up to 6 years)  Root it attached to the follicle for continued growth -> giving the root bulb a flame-shaped appearance  When pulled, may have follicle tag (translucent piece of tissue surrounding the hair’s shaft near the root – contains the richest source of DNA associated with hair -> important for individualizing hair)  Catagen phase: transition stage between the anagen and telogen phases of hair growth  Hair continues to grow but at a decreasing rate (last from 2 to 3 weeks)  Root typically take on an elongated appearance as the root bulb shrinks and is pushed out of the hair follicle  Telogen phase: final growth phase in which hair naturally falls out of the skin  Root takes a club-shaped appearance  Over 2 – 6 months, hair is pushed out of the follicle: causing hair to be naturally shed IDENTIFICATION AND COMPARISON OF HAIR  Determine whether human hair retrieved at a crime scene compared with hair from a particular individual Considerations in hair examination  Hair of various animals differs in structure that the examiner can identify the different species  Examiner must have access to a comprehensive collection of reference standards + accumulated experience of prior hair examinations  Important: scale structure, medullary index, medullary shape  Evidential value depends on the degree of probability with which the examiner can associate the hair in question with a particular individual HAIR CHARACTERISTICS  Necessary to have an adequate number of known hairs that are representative of all of its features when making a comparison  Comparing/matching the hair colour, length, and diameter  Other features including presence/absence of medulla and distribution, shape, colour intensity of pigment granules in cortex  An estimate of the time since dying/bleaching can be made because hair grows approx. 1 cm per month  Morphological abnormalities may be present because of certain diseases/deficiencies  Presence of fungal + nit infections can further link a hair to a particular individual POTENTIAL FOR ERROR  Approach is subjective and highly depends on the skill + integrity of the analyst  Microscopic hair comparisons must be regarded by police and courts as presumptive in nature + all positive microscopic hair comparisons must be confirmed by DNA determination Questions concerning hair examination  Scalp hair show little diameter variation + have more uniform distribution of pigment colour  Pubic hair are short and curly, wide v
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