Trace Evidence Hair & Fiber

Collection of Hair & Fiber Evidence

To remove a fiber from an object: Preservation/Collection of CARRIERS of hair & fiber evidence rather than the actual hairs/fibers Hair samples must also be collected from victims of suspicious deaths during autopsy To remove a fiber from an object: Use clean forceps Place it on a small sheet of paper Fold (druggist) and label paper Place packet inside another container

Hair Evidence

Hair Evidence (Class Evidence) Comparison of microscopic characteristics of questioned hairs to known hairs can provide strong corroborative evidence for placing an individual at a crime scene properly collected accompanied by adequate standard/reference samples 50 head samples 24 pubic samples

Hair Evidence – 2 Step Process Identification of Questioned Hairs Hair Examination: Animal vs Human Type of Animal Comparison of Questioned & Known Hairs

Hair Morphology Grows out of hair follicle Root – embedded in follicle Shaft – length of hair; subjected to most intense examination 3 Layers Cuticle Cortex Medulla Tip – end of hair

3 Layers of the Shaft Cuticle – scale structure covering exterior of shaft Always point towards the tip Useful in species identification Cortex – main body of hair shaft Embedded with pigment granules Color, shape, distribution of pigments provide points of comparison

3 Layers of the Shaft Medulla – cellular column running through the center of the hair Continuous Interrupted Fragmented Absent

Human Vs Animal Hairs Medullary Index Diameter of the medulla relative to the diameter of the hair shaft For Humans, less than 1/3 For Animals, usually ½ or greater Medulla Structure Uniserial Multiserial Vacuolated Lattice Amorphous Scale Patterns Coronal (crown like) Spinous (petal like) Imbricate (flattened)

Human Vs Animal Hairs Human hair exhibits ONLY an imbricate scale pattern Some humans don’t have a medulla Humans have less than 1/3 medullary index Animal hair can have all three Animals have medulla Animals have ½ or greater medullary index

Human Hair Cross-section shapes of hair can help suggest racial origin Circular Oval Flattened Body Area Determination Head hairs – longest, uniform diameter, cut tip Pubic hairs – coarse, wiry, diameter variation Facial hairs – coarse, triangular cross-section Limb hairs – short, arc-shaped, tapered

Hair Growth Anagen Phase – hair is actively growing; materials are deposited in the hair shaft Catagen Phase – transition between anagen & telogen phases Telogen Phase – resting phase; natural shedding will occur during this phase Hair forcibly removed during the Anagen Phase will exhibit a damaged root tip – follicular tag DNA Analysis of follicular tag - individualization

Fiber Evidence A fiber is a smallest unit of a textile material that has a length many times longer than its diameter

Types of Fibers (Class Evidence) Natural Fibers – derived from plant & animal sources Wool Mohair Cotton Cashmere Manufactured Fibers – man-made Regenerated Fibers – manufactured from natural raw materials Rayon Synthetic Fibers – made from synthetic chemicals Nylon Polyester

Fiber Evidence Examination Torn fabrics that can be exactly fitted in a jigsaw-puzzle type manner – individualization Microscopic Examination Color Diameter Lenghthwise striations Delustering particles (to reduce shine) Cross-Sectional shape Dye Analysis

Fiber Evidence Fibers can Occur naturally Be man-made Be spun with other fibers to form a yarn, which is woven Be knitted to form a fabric

Natural Fibers Many different natural fibers originate from plants & animals Plant Cotton Flax (linen) Jute Hemp Animal Wool Alpaca Cashmere Mohair Cotton and Wool are the most common plant and animal fibers Less common fibers have increased significance Cotton Fibers Wool Fibers

Man-Made Fibers More than half of all fibers used in production of textile materials are man-made Some man-made fibers originate from natural materials such as cotton or wood Others originate from synthetic materials

Man-Made Fibers Most common: Polyester Nylon Next most common: Acrylic Rayon Acetate The shape of a man-made fiber can determine the value placed on that fiber Some cross-sections are more common than others & unusual ones make a fiber more significant Cross-sectional views of nylon carpet fibers as seen with a scanning electron microscope (SEM)

Fiber Evidence Fiber Color Often several dyes are used to give a fiber a desired color. Individual fibers can be colored prior to being spun into yarns. How color is applied and absorbed along the length of the fiber are important comparison characteristics. Color-fading and discoloration can also lend increased value to a fiber association

Fiber Evidence Fiber Number Fiber Location The greater the number of fibers, the more likely that contact actually occurred between these individuals Fiber Location The location of fibers on different areas of the body or on specific items at the crime scene influences the significance of the fiber association

Assigning Significance When a fiber examiner matches a questioned fiber to a known item of clothing, there are only two possible explanations: The fiber actually originated from the item of clothing In order to say that the fiber originated from the item of clothing, the clothing either had to be the only fabric of its type ever produced or still remaining on earth, or the transfer of fibers was directly observed The fiber did not originate from the item of clothing Since neither of these situations is likely to occur or be known, fiber examiners will conclude that the fibers could have originated from the clothing or that the fibers are consistent with originating from the clothing.

Assigning Significance Another important consideration is coincidence. When fibers that match the clothing fibers of the suspect are found on the clothing of a victim, two conclusions may be drawn: The fibers originated from the suspect The fibers originated from another fabric source that not only was composed of fibers of the exact type and color, but was also in a position to contribute those fibers through primary or secondary contact.