Hair and Fiber Analysis

Introduction Color Structure Morphology Used to be the most useful forensic characteristics DNA is now obtained from cells in the hair root or follicle

Morphology Hair is part of the integumentary system Grows out of the hair follicle The root is embedded in the follicle Shaft extends above the surface of the skin The hair shaft is composed of three layers – cuticle, cortex and medulla Hair grows at a rate of 1 cm per month!

Cuticle Cortex Outer Cells flatten, die and keratinized Scales point away from tip of hair Identify animal from hair samples Middle Spindle-shaped cells aligned parallel to shaft Granules give hair its color

Medulla Central canal running the length of the hair Most visible feature in many animals Width of the medulla provides a means of classifying hair from different animals Medullae may be: continuous, interrupted, fragmented, or absent Medullary Index The diameter of the hair and the diameter of the medulla is measured and expressed as a fraction Humans = 1/3 or less Animals = ½ or more Human medulla are nearly absent or fragmented Human medulla are cylindrical while animals have different shapes Cats = string of pearls

Identification of Hair Scale Structure Medullary index Medullary shape Most Important!!! Overall hair color Hair length Type of medulla Information about pigment granules These things are also useful

Characteristics of Human Hair Scalp Hair = little variation in diameter and fairly uniform distribution of pigment granules, blunt because of cutting Pubic Hair = short, curly, wide variation in diameter, usually has continuous medulla Beard Hair = coarse, normally triangular or irregular in cross section Eyebrow/Eyelash Hair = short and curved, tapered tips Chest Hair = long, tapered ends, thinner diameter Underarm Hair = quite similar to pubic hair with less variations

Racial Origin Caucasoid = straight or wavy, pigment granules evenly distributed, oval or round in cross section, many shades of color Africoid = kinky, dense, unevenly distributed pigment, flat to oval in cross section Mongoloid = mostly straight, nearly circular in cross section, deeper pigmentation and thick cuticle

Hair Forcibly Removed Hair with root may have been forcibly removed Hair with root and follicular tissue probably forcibly removed

Collection of Hair at Crime Scene Flashlight and forceps useful – look everywhere Do not package hairs collected from different locations together Accurately identify the location where the hair was found, the date, and any other information that is important Examine the clothing of the victim for the presence of hairs and compare with suspect hairs Examine the clothing of the suspect for the presence of hairs and compare with the victims hairs

MacroscopicMicroscopic Length Sheen Color Straight, wavy, etc Presence or absence of follicle tissue or root Determine area from which hair came Determine if animal, plant, or human Determine racial origin Indication of dyed, bleached, etc. Diameter Medulla – continuous, fragmented or absent Scale protrusions from cuticle