forensics ch 5 & 6 notes

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Hair
Human hair is one of the most frequently found pieces
of evidence at the scene of a violent crime. It can
provide 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

Where it comes from…

shaft

root

follicle

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 patterns

Coronal – 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 Cortex

The cortex gives the hair its shape.
It has two major characteristics:

•Melanin—pigment granules that
give hair its color

•Cortical fusi—air spaces, usually
found near the root but may be
found 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 style
Determined by measuring the
diameter of the medulla and
dividing it by the diameter of the
hair.
•human hair is generally < 1/3.

•animal hair, is usually >1/2.

Hair Shape
Hair can be straight, wavy, or curly/kinky
Cross-section can be round, oval, or flattened oval

Round Oval Flattened oval
(Straight) (wavy) (curly/Kinky)

Hair Growth

Terminology
Anagen—hair is
actively growing; lasts
up to 6 years

Catagen—hair is not
growing; a resting
phase (1 – 2 weeks)
Grows about 0.4 mm per day, or
Telogen—follicle is 1 cm per month; approximately
getting ready to push ½ inch/month
the 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 Hair

Pubic 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 details
Textiles are fabrics woven in a distinctive pattern
Fabric 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 Serrate
Nylon 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

forensics ch 5 & 6 notes

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