Fiber & Hair Analysis
Hair Evidence
• Hair is composed primarily of the
protein keratin
• Defined as slender outgrowths of the
skin of mammals
• Each species of animal possesses
hair with characteristic length, color,
shape, root appearance, and internal
microscopic features that distinguish
one animal from another
• Variability exists in types of hairs
found on body of an animal
• Humans
– Head, pubic region, arms, legs & other
body areas have characteristics that
can determine their origin
• Hair types include coarse outer hairs
or guard hairs (finer fur hairs, tactile
hairs [whiskers], & others that
originate from tail & mane)
• Value of hair as evidence depends
on:
– Types of hair recovered
– Condition of hair
– # of hairs found
• Comparison of microscopic
characteristics of questioned hairs to
known hair samples helps determine
whether a transfer may have occurred
Hair Morphology
• Hair is an appendage of the skin that grows
out of an organ known as the hair folicle
• Grows from hair follicle
• Root is embedded in follicle
• Shaft has 3 parts
– Cuticle
– Cortex
– medulla
• Terminates at a tip end
Anatomy of a Hair
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Follicle
• Hair is an appendage of
the skin that grows out of
a hair follicle.
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The follicle contains more
than enough cells for simple
DNA Analysis
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Root
• The length of a hair extends
from the root embedded in
the follicle.
• A single root
contains
sufficient DNA
for analysis
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Root
• The root and other surrounding cells in
the hair follicle provide the tools
necessary to produce hair and continue
its growth.
• When pulled from the head, some
translucent tissue surrounding the hair’s
shaft near the root may be found. This
is called a follicular tag.
• By using DNA analysis on the follicular
tag, the hair may be individualized.
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Cuticle
• Is the outside covering of hair
• Gives hair resistance to chemical composition
& stability (retaining features over a long
period of time
• Formed by overlapping scales that always
point toward the tip end
• Scale pattern is useful in species identification
but not a useful characteristic for
individualizing human hair
• Variety of patterns formed by animal hair
makes it an important feature for species
identification
a) Human
b) Dog
c) Deer
d) Rabbit
e) cat
f) Horse
Cortex
• Main body of hair shaft
• The interior of the hair
• It is embedded with pigment
granules that give hair its color
• Color, shape, distribution of the
granules provide important points of
comparison
Pigment granules are absent in
grey hairs
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Medulla
• Group of cells having appearance of a
central canal running through a hair
• Sometimes it is the predominant feature,
occupying more than ½ the diameter
(varies by species)
• Medullary index is the diameter of
medulla relative to diameter of hair shaft
– Humans is less than 1/3
– Other animals, value is ½ or greater
• Presence & appearance vary between
individuals & among the hairs in a given
individual
• Medulla patterns
– Continuous
– Interrupted
– Fragmented
– Absent all together
• Human head hairs the medulla is usually
absent or fragmented; rarely have
continuous
•Animal medulla is either continuous or
interrupted
• Shape of medulla
– Cylindrical: humans & many animals
– Patterned shape: other animals
• Ex. Medulla of cat resembles a string of
pearls
• Ex. Deer medulla is spherical cells
occupying the entire hair shaft
CAT
DEER
HUMAN
DOG
RABBIT
CAT
DEER
Hair Growth
• Regions of the body that are
primarily used in forensic
comparisons are the head & pubic
areas
• As hairs undergo cyclical growth (
anagen) & resting phase (telogen),
the visible microscopic
characteristics are sufficient to
determine the phase of growth of the
hair
• Anagen phase
– Hair actively growing
– Materials are deposited in hair shaft by cells
found in follicle
– Metabolically active & dividing cells above &
around the dermal papilla of the follicle grow
upward during this phase to form – medulla,
cortex, cuticle, & root sheath
– 80-90% of hairs
• Telogen phase
– Follicle is dormant or resting
– 10-18%
• Catagen phase
– Transition period between anagen & telogen
– 2%
• Hairs routinely lost during telogen
phase & become a primary source of
evidentiary material
• Hairs can also become dislodged
from the body while they are in an
actively growing state (anagen)
• Microscope appearance of root area
will allow for the determination of
growth phase
• When pulled from the root, some
anagen hairs will have a follicular tag
– Is a translucent piece of tissue
surrounding the hair’s shaft near the
root
– Contains the richest source of DNA
associated w/hair
Naturally shed hair
- Displays undamaged, club
shaped roots
Forcibly removed hair
Forcibly removed hair
w/tissue attached
- Will exhibit stretching &
damage to root area
Comparing Strands
• The comparison microscope is an
indispensable tool for comparing the
morphological characteristics of hair.
• When comparing strands of human hair, the
criminalist is particularly interested in matching
the color, length, and diameter.
• A careful microscopic examination of hair will
reveal morphological features that can
distinguish human hair from the hair of
animals.
• Scale structure, medullary index, and
medullary shape are particularly important in
animal hair identification.
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Comparing Strands
• Other important features for comparing
human hair are:
– the presence or absence of a medulla
– the distribution, shape, and color intensity of
the pigment granules present in the cortex
• The most common request is to
determine whether or not hair recovered
at the crime scene compares to hair
removed from the suspect.
• However, microscopic hair examinations
tend to be subjective and highly
dependant on the skills and integrity of
the analyst.
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Questions
• Can the body area from which a hair
originated be determined?
• Can the racial origin of hair be
determined?
• Can the age and sex of an individual be
determined from a hair sample?
• Is it possible to determine if a hair was
forcibly removed from the body?
• Are efforts being made to individualize
human hair?
• Can DNA individualize a human hair?
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Hair Microscopy
• Done w/light microscopy
• Is a 2 step process
– ID of questioned hairs
– Comparison of questioned & known hairs
• Purpose
– To ascertain whether 2 or more individuals could
have come into contact w/an object
– Particularly useful in crimes of violence
(homicide, sexual assault, & aggravated assault)
where physical contact may have occurred
• Value of hair evidence
– Related to the variability of hair
characteristics between individuals in
the population
– Factors that impact the reliability of a
hair assoication
•
•
•
•
Experience
Training
Suitability of known hair standards
Adequacy of equipment
Hair and DNA
• Recent major breakthroughs in DNA profiling
have extended this technology to the
individualization of human hair.
• The probability of detecting DNA in hair roots
is more likely for hair being examined in its
anagen or early growth phase as opposed to
its catagen (middle) or telogen (final) phases.
• Often, when hair is forcibly removed a
follicular tag, a translucent piece of tissue
surrounding the hair’s shaft near the root may
be present.
• This has proven to be a rich source of nuclear
DNA associated with hair.
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Hair and Mitochondrial
DNA
• Mitochondrial DNA can be extracted
from the hair shaft.
• Mitochondrial DNA is found in
cellular material located outside of
the nucleus and it is transmitted only
from the mother to child.
• As a rule, all positive microscopical
hair comparisons must be confirmed
by DNA analysis.
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Collection and
Preservation
• As a general rule, forensic hair
comparisons involve either head hair or
pubic hair.
• The collection of 50 full-length hairs from
all areas of the scalp will normally ensure
a representative sampling of head hair.
• A minimum collection of two dozen fulllength pubic hairs should cover the range
of characteristics present in pubic hair.
• Hair samples are also collected from the
victims of suspicious deaths during an
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Steps in Hair Examination
Process
• Determine if hair in question is from
animal or human
• If from animal
– Identify the type of animal (species, not
specific animal)
Animal Hairs
• Hairs can vary greatly in color &
length on different areas of the body;
therefore, you should collect
reference samples from each area
• Samples should contain:
– Full length hairs
– Combings & pluckings
– If animal isn’t available for collection, a
brush or comb used on that animal
may be substituted
• Animal hairs found at scene or on
clothing may have come from a fur
coat or pelt
– Since these are usually artificially dyed
& don’t have a root, it’s preferred that
entire garment be obtained for suitable
samples
Human Hairs
• An individual sheds approximately 100 head
hairs each day
• Body area determination
– Characteristics used
• Length, shape, size, color, stiffness, curliness,
microscopic appearance, pigmentation, medullar
appearance
– Hairs that exhibit microscopic characteristics
shared by different anatomical areas are called
body hairs
• Include hair on upper legs, lower abdomen, and back
- Head & pubic hairs are used most for forensic
work because there is a wide range of
interpersonal variation in these types of hair
Head hairs
• Longest hairs on human body
• Have uniform diameter and, often, a
cut tip
• Are subject to more alteration than
hairs from other body areas
Razor-cut
hair
Hair w/cut tip
Split hair
• Alterations to natural appearance include
– Dyes, rinses, permanents, frosts
• Environmental alterations
– Excessive sunlight, wind, dryness
• Because of potential for alteration, it is
recommended that head hair samples be
obtained as soon as possible from
suspects & victims of crime
• Samples obtained years after a crime are
generally not suitable for meaningful
comparison purposes
• Known samples
– Need a random sampling of hair from
different areas of scalp
– # of hairs required vary
– General rule is to obtain at least 25 fulllength hairs, which includes both
plucked & combed, packaged
separately
Pubic Hairs
• Not subject to as much change as
head hairs over time
• Therefore, a sample taken a year or
more after a crime may still be
suitable for a meaningful comparison
• It’s recommended that known
samples be collected ASAP
• Samples should contain at least 25
full-length hairs taken from different
areas of the pubic region
• Characteristics
– Course & wiry in appearance
– Considerable diameter variation or
buckling (twisting of hair shaft)
– Often have a continuous to
discontinuous medulla
– Tapered tips are common, but these
hairs may also be abraded or cut
Hair showing buckling
Facial Hairs
• More commonly called beard or
mustache hairs
• Characteristics
– Coarse in appearance
– Have a triangular cross section
– Heavy shouldering or troughs are
observed under magnification
– Wide medulla
– Razor cut tip
• Significance of association of facial
hairs may not be as great as head &
pubic hair associations
Limb Hairs
• Hairs from legs & arms
• Characteristics
– Shorter in length, arc-like shape, often
abraded or tapered at tips, pigment is
generally granular in appearance,
medulla is trace to discontinuous
• Not routinely compared in forensic lab
• There are differences b/t individuals,
but they’re not considered sufficient to
allow limb hairs to be of value for
meaningful comparison
Fringe Hairs
• Hair originating from areas of the
body outside those specifically
designated as head or pubic
• Not suitable for significant
comparison purposes
• Examples
– Neck, sideburns, abdomen, upper leg
& back
Other body area hairs
• Not routinely compared
• Presence may help corroborate
information obtained during an
investigation (just like limb & fringe
hairs)
• Examples
– Axillary (underarm), chest, eye, nose
Racial Determination
• Head hairs are best for determining
race
• Head hair from infants can be
difficult to analyze
• Also, hairs from individuals of mixed
racial ancestry may possess
microscopic characteristic attributed
to more than one racial group
• Caucasoid
(European)
– Fine to medium
courseness
– Generally straight or
wavy in appearance
– Colors range from
blonde to brown to
black
– Hair shafts vary from
round to oval in cross
section
– Have fine to medium
sized, evenly
distributed pigment
granules
• Mongoloid (Asian)
–
–
–
–
–
–
–
–
Regularly coarse
straight
circular in x-section
Wider diameter than
other racial groups
Cuticle is usually
significantly thicker than
that of Negroid or
Caucasian hairs
Medulla is continuous &
wide
Cortex contains pigment
granules that are
generally larger in size
compared to Caucasian
hairs
Have characteristic red
appearance
• Negroid (African)
– Regularly curly or kinky
– Flattened x-section
– Can appear as curly,
wavy or coiled
– Pigment granules are
larger than those in
Mongoloid & Caucasian
– Pigments are grouped in
clumps of different
shapes & sizes
– Density of pigment in
cortex may be so great
as to make hair opaque
– Shaft has variation or
apparent variation in
diameter
– Buckling can be present
– Hair shaft frequently
splits along the lenght
Age & Sex
• Age of individual cannot be determined
definitively by microscopic examination of
hair
• However, appearance of certain hairs,
such as those of infants & elderly
individuals, may provide a general age
• How?
– Infant hair is generally finer & less distinctive
in appearance
– As one ages, hair can undergo pigment loss
& changes in configuration of hair shaft to
become much finer & more vaiable in
diameter
• Sex of individual is difficult to
determine
– However, longer treated hairs are more
frequently encountered in females
• If hair is forcibly remove, sex can be
determined using follicular tag
Treatment & Removal
• Presence of dyes or rinses can be
identified through microscopic
examination of hair
• Head hairs grow at the rate of 1cm/month
– Approximate time of treatment can be
determined by measuring the length of
untreated area
– Direct, side-by-side comparison of color of
question & known artifically treated hairs is
typically conducted by hair examiner
Biological or Environmental
Alterations
• When hairs
originated from a
body in a state of
decomposition, a
dark band may
appear near the
root of the hair
– Called postmortem
root band
Conclusions
• Several possible conclusions which can
be reached from examination &
comparison of human hair
– Questioned hair exhibits same microscopic
characteristics as know hair & is consistent
w/originating from source of known hairs
– Questioned hair is microscopically dissimilar
to hairs found in known sample & cannot be
associated to the source of known hairs
– Similarities & slight differences were observed
b/t questioned hair & known hair sample. No
conclusion could be reached as to whether
the questioned hair originated from same
source as known hairs
• When a hair exhibits same
microscopic characteristics as hairs
in known sample, a qualifying
statement may be added
– Hair comparisons are not a basis for
absolute personal identification. It
sould be noted, however, that because
it is unusual to find hairs from 2
different individuals that exhibit the
same microscopic characteristics, a
microscopic association or match is the
basis for a strong association
Significance of Hair
Evidence
•
•
•
•
•
Depends on method of collection
Processing techniques used
Methodology of hair examination
Experience of hair examiner
Head & pubic hairs are generally
viewed as more significant than
hairs from other body areas
• Certain case situations affect
significance of identifying hairs
– When a family member possibly
involved in crime
• Location, #, condition (forcibly pulled or
burnt)
– Involvement of victim’s associates
• Dates, coworkers, other people who may
have logical contact w/or access to victim
&/or crime scene
– Situations involving strangers have
greatest significance
Hair affected by burning
Textile fibers
• Can place a suspect at the crime
scene
• Fibers can be exchanged between 2
individuals, between an individual &
an object, & between 2 objects
Importance of fiber
matched to a crime scene
• When fibers are matched w/specific
source, a value is placed on that
association
• Value is dependent on:
–
–
–
–
type of fiber
Location of fibers at crime scene or on victim
# of different fibers at crime scene
# of different fibers on the victim that match
clothing of suspect
Fiber Evidence
• Fiber – smallest unit of textile
– Length much greater than diameter
– Can be naturally occurring or synthetic
– Can be spun w/other fibers to form a
yarn that can be woven or knitted to
form a fabric
Fiber Evidence
• The quality of the fiber evidence
depends on the ability of the criminalist
to identify the origin of the fiber or at
least be able to narrow the possibilities
to a limited number of sources.
• Obviously, if the examiner is presented
with fabrics that can be exactly fitted
together at their torn edges, it is a virtual
certainty that the fabrics were of
common origin.
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Fiber Evidence
• Microscopic comparisons between
questioned and standard/reference fibers are
initially undertaken for color and diameter
characteristics, using a comparison
microscope.
• Other morphological features that could be
important in comparing fibers are:
– Lengthwise striations on the surface of the fiber
– The presence of delustering particles that reduce
shine
– The cross-sectional shape of the fiber
• Compositional differences may exist in the dyes that
were applied to the fibers during the manufacturing
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process.
Transfer of Fiber
• Factors affecting transfer of fiber
–
–
–
–
Type of fiber
Length
Type of spinning method
Type of fabric construction
• Can be transferred from
–
–
–
–
Clothing
Carpets
Bed
Furniture
• Can be transferred directly (primary)
or indirectly (secondary)
• primary occurs when a fiber is
transferred from a fabric directly onto
a victim’s clothing
• Secondary occurs when already
transferred fibers on clothing of
suspect transfer to clothing of a
victim
Contact doesn’t always
transfer fibers
• Certain fabrics do not shed well
(donor garment)
• Some fabrics don’t retain fibers well
(recipient garments)
• Factors affecting retention
– Construction & composition of fabric
– Duration & force of contact
– Condition of garment w/regard to
damage
Methods For Fiber
Comparison
• The visible light microspectrophotometer is a
convenient way for analysts to compare the
colors of fibers through spectral patterns.
• A more detailed analysis of the fiber’s dye
composition can be obtained through a
chromatographic separation.
• Infrared spectrophotometry is a rapid and
reliable method for identifying the generic class
of fibers, as does the polarizing microscope.
• Depending on the class of fiber, each polarized
plane of light will have a characteristic index of
refraction.
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Collection and Preservation
• The investigator’s task of looking for minute
strands of fibers often becomes one of
identifying and preserving potential “carriers”
of fiber evidence.
• Relevant articles of clothing should be
packaged carefully in separate paper bags.
• If it is necessary to remove a fiber from an
object, the investigator must use clean
forceps, place it in a small sheet of paper, fold
and label the paper, and place the paper
packet inside another container.
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Types of Fibers
• Natural fibers are derived in whole from
animal or plant sources.
– Examples: wool, mohair, cashmere, furs, and
cotton.
• Man-made fibers are manufactured.
– Regenerated fibers are manufactured from
natural raw materials and include rayon,
acetate, and triacetate.
– Synthetic fibers are produced solely from
synthetic chemicals and include nylons,
polyesters, and acrylics.
• Polymers, or macromolecules, are
synthetic fibers composed of a large
number of atoms arranged in repeating
units known as monomers.
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Natural Fibers
• Originate from plants or animals
• Common plant fibers
– Cotton, flax (linen), ramie, rayon, sisal, jute,
hemp, kapok (silky-cotton like substance), &
coir (coconut fibers)
• Common animal Fibers
– Wool (usually from sheep), camel, alpaca,
cashmere, mohair
– End use of sheep’s wool dictates fineness or
coarseness of fibers
• Finer fibers used in clothing
• Coarser fibers found in carpet
– Fiber diameter & degree of scale protrusion
are important characteristics
Cotton fibers
Wool fibers
Flax fibers
Ramie fibers
Kapok fibers
Hemp fibers
Cotton- Hemp Blend
Synthetic Fibers
• More than ½ of all fibers used in
production of textile materials are
synthetic
– Polyester, nylon, acrylics,acetates
• Some originate from natural
materials such as cotton or wood
• Amount of production of particular
synthetic fiber & its use influence the
degree of rarity of a given fiber
• Shape of synthetic fiber can
determine the value placed on the
fiber
Cross section of synthetic
fibers
Cross section of different
nylon fibers
Fiber Color
• Influences value given to a particular
fiber identification
• Often several dyes are used to give
a fiber a desired color
• Individual fibers can be colored prior
to being spun into yarn
• Yarns can be dyed , & fabrics made
from them can be dyed
• Color can be applied to surface of
fabric – as in printed fabrics
• How color is applied & absorbed
along length of fiber are important
comparison charateristics
• Color-fading & discoloration can also
lend increased value to a fiber
association
Fiber Number & Location
• # of fibers on clothing of a victim
identified as matching clothing of
suspect is important in determining
actual contact
– Greater the # of fibers, the more likely
that contact actually occurred
• Location of fibers on different areas
of body or on specific items at scene
influences the significance of the
fiber association
Fabric Type
• How fabric is constructed affects the # &
types of fibers that may be transferred during
contact
– Tightly woven or knitted fabrics shed less than
loosely knit or woven fabrics
– Fabrics composed of filament yarns shed less
than fabrics composed of spun yarns.
• Age of fabric affects degree of transfer
– Newer fabrics may shed more readily because of
an abundance of loosely adhering fibers on
surface
– Worn fabrics may have damaged areas that easily
shed fibers
– Damage to fabric caused during physical contact
greatly increases the likelihood of fiber transfer
Fabric Source
Determination
• It is not possible to say positively
that a fiber originated from a
particular fabric
• inability to positively associate a
fiber w/a source in no way
diminishes the significance of a fiber
association
• It’s very helpful to know frequency of
occurrence f a particular fabric &
fiber, or how many fabrics w/a
particular fiber type & color exist, as
well as who owns them
• If manufacture is known, possibility
exists that # of fabric units produced
could also be obtained
• Once a particular fiber of a certain
type, shape, & color is produced &
becomes part of a fabric, it occupies
an extremely small portion of the
fiber/fabric composition
• Exception – white cotton & blue
cotton fibers (blue jeans)
Fiber Transfer &
Persistence
• Depends on type of fabric, & nature
& duration of contact
• Transferred fibers are usually lost
rather quickly – depends on type of
fabric & movement after contact
• Clothing of homicide victim would
tend to retain transferred fiber for a
longer period because victim is not
moving
• EMS, medical examiners &
investigators must handle victim’s
clothing carefully to minimize fiber
loss
• Fibers will be lost is if victim/suspect
moves about, brush the clothing or
wash it
• Nature of contact
– Can determine the # of fibers transferred & value
placed on their discovery
– Violent physical contact of an extended duration
will very often result in numerous fiber transfers
• Multiple fiber associations
– Multiple fiber types found on different items of
clothing or fabric from suspect, victim, or scene
greatly increase the likelihood that contact
occurred between those individuals & the scene
– Each associated fiber is considered to be an
independent event
– Multiple associations undermine a coincidence
defense
Fiber Evidence: Assigning
Significance
• Matching dyed synthetic fibers or dyed
natural fibers can be very meaningful
• Whereas, matching of common fibers,
such as white cotton or blue denim
cotton would be less significant
• Discovery of cross transfers & multiple
fiber transfers between suspect’s
clothing & victim’s clothing dramatically
increasesthe likelihood that these 2
individuals had physical contact
• When a fiber examiner matches a
questions fiber to a know item of
clothing, there are only two possible
explanations
– Fiber actually originated from the item
of clothing
– Fiber did not originate 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 biers was directly
observed
• therefore, fibers examiners will
conclude that the fibers could
have originated from the clothing
or that the fibers are consistent
with originating from the clothing
• Only way to say that a fiber did not
originate from a particular item of
clothing is to know the actual history
of the garment or to have actually
observed the fiber transfer from
another garment
Paint
• Paint spread onto a surface will dry into a
hard film that can best be described as
consisting of pigments and additives
suspended in the binder.
• One of the most common types of paint
examined in the crime laboratory involves
finishes emanating from automobiles.
• Automobile manufacturers normally apply
a variety of coatings to the body of an
automobile.
• These coatings may include electrocoat
primer, primer surfacer, basecoat, and
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Methods For Paint
Comparison
• The wide diversity of automotive paint contributes to
the forensic significance of an automobile paint
comparison.
• Questioned and known specimens are best
compared side by side under a stereoscopic
microscope for color, surface texture, and color layer
sequence.
• Pyrolysis gas chromatography and infrared
spectrophotometry are invaluable techniques for
distinguishing most paint binder formulations, adding
further significance to a forensic paint comparison.
• Crime laboratories are often asked to identify the
make and model of a car from a small amount of
paint and will make use of color charts for automobile
finishes.
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Collection and Preservation
• Paint chips are most likely found on or near persons
or objects involved in hit-and-run incidents.
• Paper druggist folds and glass or plastic vials make
excellent containers for paint.
• Paint smeared or embedded in garments or objects
require the whole item to be packaged and sent to
the laboratory.
• Uncontaminated standard/reference paint must
always be collected.
• Tools used to gain entry into buildings or safes often
contain traces of paint, requiring the tool be collected,
along with reference paint samples.
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