7th Grade Forensic Science

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Hairs Fibers

• 7th Grade Forensic Science

http//media.popularmechanics.com/images/PMX0706FO
RENSICSHairSmall.jpg
Presentation developed by T. Trimpe 2006
http//sciencespot.net/
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Hair Evidence
Hair is one of the most common forms of trace
evidence The examination of human hairs in the
forensic laboratory is conducted through the use
of light microscopy. The examination involves the
identification of questioned hairs and the
comparison of questioned and known hairs.
The first step in the hair examination process is
to determine whether the hair in question
originated from an animal or a human. If the
hair originated from an animal, it is possible to
further identify it to a particular species of
animal. It is not possible to identify hairs to a
specific animal to the exclusion of other similar
animals. An example of this occurs when dog hairs
can be associated to a particular breed but
cannot be identified to a specific dog within
that breed.
A scientist using a comparison-light microscope
View of matching hairs using a comparison-light
microscope
What characteristics help investigators identify
hair samples?
http//www.fbi.gov/hq/lab/fsc/backissu/july2000/de
edric1.htmIndex20(Hairs)
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Biology of Hair Hair is an outgrowth of the skin
and is produced from a structure called the hair
follicle. Humans develop hair follicles during
fetal development, and no new follicles are
produced after birth. Hair is composed of the
protein keratin. Keratin is also the primary
component of finger and toe nails.
Hair color is mostly the result of pigments,
which are chemical compounds which reflect
certain wavelengths of visible light. Hair color
may also be influenced by the optical effects of
light reflecting and bouncing off the surfaces of
the different hair.
Hair shape (round or oval) and texture (curly or
straight) is influenced heavily by genes.
Nutritional status and intentional alteration
(heat curling, "perms") can affect the physical
appearance of hair.
The body area from which a hair originated can be
determined by the samples length, shape, size,
color, stiffness, curliness, microscopic
appearance, pigmentation, and the appearance of
the medulla. Hairs that exhibit similar
characteristics from different areas on the body
are often referred to as body hairs and include
hairs found on the upper legs, lower abdomen, and
back.
Sources http//library.thinkquest.org/04oct/00206
/lesson.htmt_hair http//www.fbi.gov/hq/lab/fsc
/backissu/july2000/deedric1.htmIndex20(Hairs)
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Hair Structure
Hair is composed of three principal parts
Cuticle outer coating composed of overlapping
scales
The structure of hair has been compared to that
of a pencil with the medulla being the lead, the
cortex being the wood and the cuticle being the
paint on the outside.
http//library.thinkquest.org/04oct/00206/lesson.h
tmt_hair
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• Cuticle
• The scales of the cuticle may vary in
• How many there are per unit of measure
• How much they overlap
• Their overall shape
• How much they protrude from the surface
• The thickness of the cuticle may vary as well,
  and the cuticles of some species' hairs may
  contain pigment.
• Characteristics of the cuticle may be important
  in distinguishing between hairs of different
  species but are often not useful in
  distinguishing between different people.

http//library.thinkquest.org/04oct/00206/lesson.h
tmt_hair
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• Cortex
• The cortex varies in
• Thickness
• Texture
• Color
• Distribution of pigments
• The cortex is perhaps the most important
  component in determining from which individual a
  human hair may have come. Microscopic examination
  can also reveal the condition and shape of the
  root and tip.

http//library.thinkquest.org/04oct/00206/lesson.h
tmt_hair
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• Medulla
• The medulla may vary in
• Thickness
• Continuity - one continuous structure or broken
  into pieces
• Opacity - how much light is able to pass through
  it
• It may also be absent in some species.
• Like the cuticle, the medulla can be important
  for distinguishing between hairs of different
  species, but often does not lend much important
  information to the differentiation between hairs
  from different people.

http//library.thinkquest.org/04oct/00206/lesson.h
tmt_hair
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Hair Evidence Review

• Hair is one of the most common forms of trace
  evidence, but is not the best type of physical
  evidence for establishing identity. It is not
  possible to show with any certainty that two
  hairs came from the same person or animal.
• However, hair can be used to rule out certain
  suspects or scenarios. It can also be used to
  corroborate (support) other physical evidence if
  it is consistent with the rest of the evidence.
• A strand of hair has three distinctive parts
  cuticle, cortex, and medulla. By examining these
  parts as well as pigmentation and other features
  an investigator can compare hair samples from a
  crime scene.
• Hair can be used for DNA testing.
• The hair follicle, which is in the base of hair,
  contains live cells with DNA material and must be
  present for DNA testing.
• For using it in analysis of DNA (paternity tests,
  crime investigations, etc), the hair must be
  uprooted.
• The hair which falls as breakage isn't useful
  since it doesnt have a root.

http//library.thinkquest.org/04oct/00206/lesson.h
tmt_hair
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Fiber Evidence
A fiber is the smallest unit of a textile
material that has a length many times greater
than its diameter. Fibers can occur naturally as
plant and animal fibers, but they can also be
man-made. A fiber can be spun with other fibers
to form a yarn that can be woven or knitted to
form a fabric. The type and length of fiber
used, the type of spinning method, and the type
of fabric construction all affect the transfer of
fibers and the significance of fiber
associations. This becomes very important when
there is a possibility of fiber transfer between
a suspect and a victim during the commission of a
crime.
Matching dyed synthetic fibers or dyed natural
fibers on the clothing of a victim to fibers on a
suspects clothing can be very helpful to an
investigation, whereas the matching of common
fibers such as white cotton or blue denim cotton
would be less helpful. The discovery of cross
transfers and multiple fiber transfers between
the suspect's clothing and the victim's clothing
dramatically increases the likelihood that these
two individuals had physical contact.
http//www.fbi.gov/hq/lab/fsc/backissu/july2000/de
edric3.htmFiber20Evidence
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Types of Fibers
Many different natural fibers originating from
plants and animals are used in the production of
fabric.
http//www.fbi.gov/hq/lab/fsc/backissu/july2000/de
edric3.htmFiber20Evidence
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Grab a microscope!
It's time to investigate!