Hair as Evidence Form Structure of Hair Hair

Hair as Evidence Form & Structure of Hair

Hair as Evidence Hair is frequently found at a crime scene Locard Exchange Principle Hair is considered class evidence Could possibly be individualized if root tissue is still attached to the hair Very useful in supporting circumstantial evidence Can be used to place someone at the crime scene Can link a criminal with the crime

Hair as Evidence From hair, one can determine: If the source is human or animal Race o Sometimes § Based on shape of hair Origin of the location on the source’s body Whether the hair was forcibly removed o By whether or not root attached Whether the hair has been treated with chemicals If drugs have been ingested

Interesting Hair Facts Human body has about 5 million hairs o Most are downy hair covering body Hair is continuously shed & renewed throughout lifetime o About 100/24 hour period on head alone § Much higher rate of loss for body hair Hair on the head o Blonds have most – about 120, 000 strands o Redheads have least – about 80, 000 strands o Black/Brown in the middle – about 100, 000 strands

Hair Morphology Must understand structure of hair to analyze it Made up of cross-linked protein polymers o Very resistant to breaking down Grows from a tube-like organ called a follicle o Located in the dermis

Hair Morphology Follicle is linked to the body’s blood supply o Whatever is taken into body is distributed to part of hair growing at that time o Important in analyzing hair for drugs & poisons Hair shaft extends through epidermis & ends at tip o Shaft composed of dead cells

Hair Shaft Composed of three parts: o. Cuticle §Clear, outer covering of shaft §Made of tough, overlapping scales Scales finer in humans compared to animals o. Cortex §Made of protein called keratin §Embedded with pigment that gives hair color §Contains air sacs called cortical fusi Different shapes & sizes v. Possible class characteristic o. Medulla §Canal running down center of cortex §May be dark or translucent depending on contents

The Cuticle Outer most layer of hair covered with scales Scales point toward tip of the hair Scales differ among species of animals o Named based on their appearance Three basic scale patterns include: o Coronal § Mouse o Spinous § Cat o Imbricate § Human

Human Scales To visualize scales: Paint clear fingernail polish on a glass slide. When the polish begins to dry, place a hair on the polish. When it is almost dry, lift off the hair and observe the scale imprints. What pattern is seen in this slide?

The Cortex Gives hair its shape Has two major characteristics: o. Melanin is pigment that gives hair its color §Produced by melanocytes located in the follicle o. Cortical fusi are air spaces usually found near the root §Sometimes found throughout the cortex

The Medulla May be dark or translucent o Depends on whether it contains air, liquid, or pigment May be continuous, interrupted, or fragmented Human hair usually lack a medulla or has one that is fragmented o Except for Native Americans & Asians whose hair have a continuous medulla Animal hairs have wide variety of medullar patterns o Patterns can identify some species

The Medulla Hair’s core that is not always visible Comes in different types and pattern Patterns Include: o. Interrupted o. Fragmented o. Continuous o. Stacked o. Absent

Human Medulla Human medulla may be continuous, fragmented, or absent

Medullary Index Determined by measuring the diameter of the medulla then dividing it by the diameter of the hair o MI = medulla diameter x 100 hair diameter o Medullary index for human hair is generally <33 o Medullary index for animal hair is generally >50

Medullary Index Deer MI = 100 Raccoon MI = 80 Human MI = 25

Hair Shape May be straight, curly, or kinky Round (Straight) o. Depends on the cross-section Cross-section may be: o Round o Oval o Crescent-shaped: Oval (Curly) Crescent moon (Kinky)

Hair Shape by Race Asians & Native Americans o Round cross section & no twisting Undulated Twisted Caucasians, Mexicans, & Middle Eastern heritage o Oval cross section & rarely twist o Evenly distributed pigmentation African heritage o Crescent-shaped cross section with a twist o Dense, clumped pigmentation

British CSI School Hair & Fiber Analysis