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HairHuman hair is one of the most frequently found piecesof evidence at the scene of a violent crime. It canprovide a link between the criminal and the crime.From hair, one can determine:• If the source is human or animal• Race (sometimes)• Origin of the location on the source’s body• Whether the hair was forcibly removed• If the hair has been treated with chemicals• If drugs have been ingested
It’s what’s inside that counts…Composed of: Hair Shaft Cuticle—outside covering, made of overlapping scales Cortex—inner layer made of keratin and embedded with pigment; also contains air sacs called cortical fusi Medulla—inside layer running down the center of the cortex
The Cuticle• outermost layer of hair• covered with scales• scales point toward the tip of the hair• Scales differ among species of animals and are named based on their appearance.
The Cuticle – 3 basic patternsCoronal – small Spinous – minks,rodents, bats seals, cats Imbricate – human and large mammals
Viewing the Cuticle In order to visualize the 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 CortexThe cortex gives the hair its shape. It has two major characteristics:•Melanin—pigment granules thatgive hair its color•Cortical fusi—air spaces, usuallyfound near the root but may befound throughout the hair shaft
The Medulla The medulla is the hair core that is not always visible. The medulla comes in different types and patterns.Types: Interrupted Fragmented Continuous Absent—not present
Medullary Index Click to edit Master title styleDetermined by measuring thediameter of the medulla anddividing it by the diameter of thehair.•human hair is generally < 1/3.•animal hair, is usually >1/2.
Hair ShapeHair can be straight, wavy, or curly/kinkyCross-section can be round, oval, or flattened oval Round Oval Flattened oval (Straight) (wavy) (curly/Kinky)
Hair GrowthTerminologyAnagen—hair isactively growing; lastsup to 6 yearsCatagen—hair is notgrowing; a restingphase (1 – 2 weeks) Grows about 0.4 mm per day, orTelogen—follicle is 1 cm per month; approximatelygetting ready to push ½ inch/monththe hair out; lasts 5 –6 weeks
The Root• Human roots look different based on whether they have been forcibly removed or they are telogen hairs that have fallen out.• Animal roots vary, but in general have a spear shape. Fallen out Forcibly removed
Origin of the Hair Head Hairs Pubic Hairs• Long with moderate shaft • Shaft diameter coarse with diameter and diameter variation wide variations and buckling• Medulla absent to continuous • Medulla relatively broad and and relatively narrow when usually continuous when compared to the structure of present hairs from other body areas• Often with cut or split tips • Root frequently with tag• Can show artificial treatment, • Tip usually tapered, rounded, solar bleaching, or mechanical or abraded damage • Stiff texture, wiry• Soft texture, pliable
Origin of the HairPubic Hair Buckling Pubic Hair Root with Tag
Comparing Hair The following features of hair can be used as points of comparison:• Color • Scale types• Length • Presence or absence• Diameter of medulla• Distribution, shape, and color • Medullary type intensity of pigment granules • Medullary pattern • Dyed hair has color in cuticle and cortex • Medullary index • Bleaching removes pigment and gives a yellow tint
DNA from Hair• The root contains nuclear DNA. If the hair has been forcibly removed, some follicular tissue containing DNA may be attached.• The hair shaft contains abundant mitochondrial DNA, inherited only from the mother. It can be typed by comparing relatives if no DNA from the body is available. This process is more difficult and more costly than using nuclear DNA.
The Collection of Hair Questioned hairs must be accompanied by an adequate number of control samples.• From victim• From possible suspects• From others who may have deposited hair at the scene • 50 full-length hairs from all areas of scalp • 24 full-length pubic hairs
Limitations of Hair Analysis• Unless DNA is collected, hair is usually class evidence• Evidence may be consistent with a known sample• Hair can vary within a hair and among hairs on the head
Hair Toxicology Advantages:• Easy to collect and store• Is externally available• Can provide information on the individual’s history of drug use or evidence of poisoning Collections must be taken from different locations on the body to get an accurate timeline.
• Like hair, fibers are commonly Fibers found at crime scenes• Usually class evidence but can provide associations and connections
Fibers - the detailsTextiles are fabrics woven in a distinctive patternFabric is made of fibers.Fibers are made of filaments.Filaments Natural - animal, vegetable, or inorganic Artificial – made form altered natural sources
Points of Comparison:• Types of filaments Fabric• weave• degree of stretch• water repellence• absorbency• softness• durability
Filament Cross Sections• Synthetic fibers are forced out of a nozzle when they are hot, and then they are woven.• holes of the nozzle are not always round• filaments may have a unique shape in cross section. R ound 4-lobed Octalobal T rilobal Irregular Dogbone or Multi-lobed Dumbbell or SerrateNylon carpet fibers in cross-section
Collecting Fibers• Bag clothing• Use tape lifts to gather fibers• Use tweezers, tape, or a vacuum• Collect exemplars of known fibers/fabrics