Impressions and Tool Marks - 2
Impressions and Tool Marks - 2
Impressions and Tool Marks - 2
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Tool
Marks
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What is a Tool Mark?
A tool mark is considered
to be any impression, cut,
scratch, gouge, or
abrasion caused by a tool
coming into contact with
another object.
For example, if you
attempted to pry open a
locked window with a
screwdriver, the
screwdriver would leave a
tool mark on the window
and windowsill.
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Usually Involve Forcible Entry
Most often, tool marks are encountered
at burglary scenes that involve forcible
entry into a building or safe.
Typically, an indented impression is left
on the frame of a door or window as a
result of the prying action of a
screwdriver or crowbar.
One of the first things an investigator
looks for at a suspects home is the
suspects toolbox.
Any tools in the commission o f a crime
leave unique scratch marks behind.
These striation marks can be used to
match a tool to an object it came into
contact with at the crime scene.
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A careful examination of these impressions can
reveal important class characteristics. . .
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The Machining Process
Such markings are left as a result
of the machining processes used to
cut and finish tools.
These markings are called striation
marks.
The shape and pattern of such
minute imperfections are further
modified by damage and wear
during the life of the tool.
When a screwdriver is first made,
the microscopic imperfections in
the blade make it unique.
As it is used, more imperfections
are added and the blade becomes
more unique.
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Imperfections Cause Individuality
Considering the unending
variety of patterns that
the hills and valleys can
assume, it is highly
unlikely that any two
tools will be identical.
Hence, it is the presence
of these minute
imperfections that
imparts individuality to
each tool.
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One of the major
problems associated
with tool mark
comparisons is the
difficulty in
duplicating in the lab
the tool mark left at
the crime scene.
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Striations
If the edge of a tool is
scraped against a softer
surface, it may cut a
series of striated lines
that reflect that pattern
of the tools edge.
Markings left in this
manner are compared in
the lab through a
comparison microscope
with test tool marks
made from the suspect
tool.
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Positive Comparisons
Once at the crime lab, a
cast is made of the scratch
marks left on the window
lock from the forced entry.
The result can be a positive
comparison, and hence a
definitive association of the
tool with the evidence mark,
when a sufficient quantity
of striations match between
the evidence and test
markings.
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Test Marks
A thorough comparison requires the
preparation of a series of test
marks obtained by applying the
suspect tool at various angles and
pressures to a soft metal surface
(lead is commonly used).
The cast and the lead brick with
the scrapings are placed under a
comparison microscope to see if the
striation marks match.
This approach gives the examiner
ample opportunity to duplicate many
of the details of the original
evidence markings.
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Bring the entire object to the
crime lab.
Whenever practical, the
entire object or part of
the object bearing a tool
mark should be
submitted to the crime
lab for examination.
When removal of the
tool mark is impractical,
the only recourse left, is
to photograph the
marked area to scale and
make a cast of the mark.
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Photograph the mark.
However, even under the
most optimum
conditions, the clarity of
many of the tool marks
minute details will be
lost or obscured in a
photograph or cast.
Of course, this will
reduce the possibility
that the criminalist
could individualize the
mark to a single tool.
14
Use liquid silicone or dental stone
for casting.
Under these
circumstances, liquid
silicone casting
material or dental
plaster has been
found to be the most
satisfactory for
reproducing most of
the fine details of the
mark.
15
Under no circumstances . . .
Must the crime scene
investigator attempt
to fit the suspect tool
into the tool mark.
Any contact between
the tool and the
marked surface may
alter the mark and
will, at the least, raise
serious questions
about the integrity of
the evidence.
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The Lindbergh Baby
Kidnapping
In 1932 the infant son of
Charles and Ann
Lindbergh was kidnapped
from his nursery. A
handmade wooden ladder
used to gain entrance to
a second-floor window, a
ransom note, some muddy
footprints, and a chisel
were the only clues left
at the crime scene.
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The ransom was paid, but the infant was
never returned.
His body was eventually found in the woods
near the Lindbergh home.
A suspect, Richard Hauptmann, was
eventually arrested.
One of the first things forensic
investigator, Arthur Koehler looked for
was Richard Hauptmanns toolbox. . .
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In it he found . . .
The hand plane used to construct the homemade
ladder.
The imperfections in the planes blade caused
unique striation marks on any wood it was used on.
Test pieces of wood planed with this tool
displayed the same striation marks found on the
wooden ladder left at the Lindbergh home.
This proved that Richard Hauptmanns plane was
used to make the ladder used in the kidnapping.
The wood used to make the ladder used in the
infants kidnapping was also matched to Richard
Hauptmanns attic.
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Packaging
The suspect tool and
mark must be packaged in
separate containers,
with every precaution
taken to avoid contact
between the tool or mark
with another hard
surface.
Failure to properly
protect the tool or mark
from damage could result
in the destruction of its
individual characteristics.
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Furthermore
The investigator must
bear in mind that the
tool or its impression
may contain valuable
trace evidence.
Chips of paint adhering
to the mark or tool
provide perhaps the
best example of how the
transfer of trace
physical evidence can
occur as a result of
using a tool to gain
forcible entry into a
building.
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Obviously
The presence of trace
evidence greatly
enhances the
evidential value of the
tool or its mark and
requires that special
care be taken in the
handling and packaging
of the evidence to
avoid the loss or
destruction of these
items.
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Impressions
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Impressions can sometimes be
discovered in the most unusual
places.
A man was found dead in the early
morning hours on the side of a road in
Binghamton, NY the responding police
officers could tell just from the condition
of the body that he had been the victim
of a hit and run accident.
There had been a rainstorm that night,
so no tire tracks were visible. . .
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There was also an absence of
any skid marks . . .
Indicating that the driver had not
stopped for the pedestrian.
In a search of the crime scene the police
noticed a van parked on the side of the
road, and on closer inspection, saw that
there was a man asleep behind the
wheel. . .
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The police knocked on the car
window and proceeded to
question
thethat
He explained driver . .out
he was . driving in
the early hours of the morning and was
too tired to make it home.
The rain was also a factor in his decision
to pull over and rest.
He said that he had almost fallen asleep
and lost control of the van.. . .
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It had fishtailed in the
driving rain . . .
And when he regained
control of the vehicle, he
decided to pull over and
get some sleep.
When the police looked at
the other (passenger) side
of the van, they were
shocked to see the
impression of the
pedestrian in the side of
the van.
The driver did not even
know that he had struck
someone.
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Another Story . . . Of
toolmark blunders and
the use of forensic
impressions. . . .
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The steering column of a stolen vehicle
had been broken open with some type of
tool in order to reach the ignition and
disable the steering wheel lock.
A suspect located near the vehicle was
found to have a screwdriver in his
backpack.
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The investigating officer submitted the
steering column to the crime lab along
with the screwdriver to see if it might
have been used in the crime . . .
The steering column was examined, and
an area of striated tool marks was found
on a small internal part.
30
A cast of the
questioned tool mark
was obtained using a
dental rubber casting
medium so that the
tool mark could be
examined
microscopically (its
tough to put a
steering column
under a microscope!).
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Spacing between teeth in gripping
or cutting instruments can play a
major role in forensic tool mark
examinations.
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A tool mark
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Evidence Collection of
Impressions
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There are three materials
commonly used in forensic
science to make casts of tool
marks and other impressions:
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1. Dental Stone
A very fine grade of calcium sulfate (known as alginate,
gypsum, or Plaster of Paris) that was developed for
dentists to take dental impressions.
Dental stone is normally the material of choice when
making a cast of bite marks, shoeprints, and tire
prints.
Dental stone is prepared by mixing about 2 parts
alginate with 1 part water.
The resulting paste is applied to the impression
and allowed to set for a few minutes to a few hours
depending on size and temperature.
Chromatic dental stone changes color, letting you
know when to apply the paste and when it has set.
In snow, a waxy substance called Snow Print Wax is
first sprayed over the impression, and then the cast is
made.
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2. Permlastic
3. Polyvinylsiloxan
Are both used to take the impressions of
smaller objects like bite marks or scratches left
behind on a forced lock.
Both products consist of two tubes (base and a
catalyst), which are connected so that equal
amounts of each are dispensed.
The two components are mixed, and the paste
is applied to the impression.
Both compounds polymerize in about hour to form an
elastomeric (rubbery) solid which can then be peeled off
the object.
Both take extremely fine impressions.
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Footwear can also leave
valuable impressions and prints
behind at the crime scene.
An electrostatic dust lifter can be used to
charge a plastic film that has been placed over
a footwear impression.
The charged plastic lifts any dust particles from
the impression, and they adhere to the film.
These devices work best in a dry environment.
Work well on paper, wood, carpet, linoleum,
and concrete.
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If a footprint is in a mud puddle, you
may use a turkey baster to drain
excess water and use powder to dry the
area before casting the print.
Casts must be carefully packaged in a
soft resilient material that would
prevent breakage, such as cotton or
Styrofoam, etc. It is helpful to secure
the cast so that it will not move during
transport.
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There are many Internet sites that
provide data for matching footwear prints
and tire track impressions to the
manufacturer.
http://members.aol.com/varfee/mastssi
te/index.html
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Footprint Cast Inked
Footprint
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Once the print or impression
has been taken, the forensic
scientist can develop a great
deal of class characteristic
Measurements of the length and width of
evidence.
footwear can be used to calculate the size of a
shoe.
The pattern produced by the sole of the shoe
can be used to determine the manufacturer.
A footwear print about 11.5 inches long and
about 4.3 inches wide might indicate a size 8
D shoe.
42
The tread patterns are often
specific to different
manufacturers.
Many popular sneaker manufacturers
actually put the name of the company
(Addias, for example) in the tread
design or the company symbol
(Reebok often includes its two lines
with a third intersecting logo).
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Once the suspect is
apprehended, the forensic
investigator is often asked if a
positive match can be made
between the suspects footwear
All shoes of a certain type are the same
and the print left behind at the
when they come off the production line.
crime scene.
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However, once a person starts
wearing a shoe, random and
unique wear patterns begin to
appear.
Some people put more pressure on one
side of the foot than on the other, and
the tread picks up cuts, scrapes, and
foreign objects, which can make each
footprint unique.
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The forensic scientist takes the
suspects footwear, inks it on a
pad, and presses it against a
piece of white paper much as in
taking
a persons
The print is comparedfingerprint.
to any left at the
crime scene, and a point-by-point match
can be presented to the court just as in
the case of a fingerprint
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Tire Track
Impressions
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Tire Impressions
Design Elements:
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Tire Impressions
Noise Treatment:
If tire design was exactly repeated around
the tire, noise would result.
Design repeated at different pitch lengths
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Tire Impressions
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Tire Impressions
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Tire Impressions
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Tire Impressions
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Tire Impressions
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Tire Impressions
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Tire Impressions
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Tire Impressions
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C.A.S.T. Website
address:http://members.aol.co
m/varfee/mastssite/index.html
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An identical process can also be
used for a tire track print or
impression.
The width of the tread impression gives the
first number in the size of a tire.
For example, the tire size 235/60R16 stands for a tire
that has a 235 mm wide tread with an aspect ratio
(the ratio of the height of the sidewall of the tire to
the width of the tread divided by 100) of 60.
It is also a radial and fits on a 16 inch diameter
wheel.
Multiplying the decimal aspect ratio (the aspect ratio
divided by 100) by the width of the tire gives the
height of the sidewall of the tire.
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A tire impression left at a crime scene
that was about 9.3 inches wide and
showed a repeating imperfection mark
every 84.7 inches of travel is
consistent with this size tire .
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To prove this, the width can be converted
from inches to mm by multiplying by 25.4
mm/in.
Width (mm) = width (in) X 25.4
mm/in
= 9.3 inches x 25.4 mm/in = 236 mm
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Tire sidewall height
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Tire Diameter
sidewall height
= 16 inches + 2 x 5.6 = 27.2 inches
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Tire Circumference
diameter
3.14 x 27.2 inches = 85.4
inches
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Any imperfections in the tire tread would
be expected to repeat every 85.4 inches,
which is consistent with what was found
at the crime scene.
Exact widths and diameters of tires vary
depending on the manufacturer and on
inflation, so the numbers are always
approximate.
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Tread patterns are often unique,
and patented, for each
manufacturer, so a brand of tire
can often be determined from
the tread pattern.
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As the vehicle is driven, the
tires develop unique wear
patterns.
Some wear faster on the front tires, and some
on the back.
Wear can take place more on the inside of the
tires, the middle, or the outside, and wear may
show scalloping along the edges.
There may be random cuts, nicks, or stones in
the tread.
These all leave unique impressions at the crime
scene that can be used to positively associate
the vehicle with the crime.
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Dental Forensics
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Bite Mark Evidence
Investigators can analyze bite marks for characteristics to help them
identify victims or suspects as well as to exclude others. Marks can
be left on a victims skin or other objects, such as Styrofoam cups,
gum, or foods. Saliva or blood may be left behind that can be tested Bite Mark Evidence Video
for DNA. Dental records including x-rays can also provide useful
information, especially when attempting to identify a victim.
Features to analyze:
Type of bite mark (human or animal)
Characteristics of the teeth (position, evidence of dental work, wear
patterns, etc.)
Color of area to estimate how long ago the bite occurred (old or
recent bite)
Swab for body fluids for DNA tests
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People can be identified by their teeth
because everyones teeth are different.
Since almost everyone has been to a dentist,
most people have a dental record.
This makes teeth a better identifier than
fingerprints, since many people have never been
fingerprinted.
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Teeth are unique to the
individual. Items to look for:
Restorations amalgam, gold, resin,
porcelain
Fillings location, size, and shape
Gums
Root canals
Missing teeth
Unerupted teeth
Patterns of arrangement
Appliances, dentures
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Teeth are extremely resistant to
decomposition and damage.
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Impressions made of teeth, look different
from one another, particularly if a person
has missing teeth or fillings.
Criminalists can use tooth impressions
to identify the perpetrator of a crime by
matching an impression of his teeth with
the marks he leaves (i.e. in a piece of
gum, cheese, an apple, or on a victim, or
even old bite marks can be used because
they show up under ultraviolet light).
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Why identify?
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Fun Fact!
The first recorded American use of forensic
dentistry to make a positive ID was in the case of
Dr. Joseph Warren.
He was thought to have died in the Battle of
Bunker Hill.
Skeletal remains were found with a dental implant.
The implant was made of silver and was taken to
the silversmith who was thought to have made it.
This mad admitted to having personally crafted it
for Dr. Warren.
The silversmiths name was Paul Revere.
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The most famous bite mark
case . . .
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Naming Victims
Forensic dentists play an important role in
identifying the remains of victims from mass
disasters, such as those in the 1995 bombing
of the Oklahoma City federal building.
Dentists from across the country helped
identify 25% of the human remains from the
1994 disaster.
In a similar case, dentists helped identify many
of the victims from the 1994 crash of American
Eagle ATR 72 in Indiana.
Even though only 9% of the victims teeth were
recovered from the crash, those teeth were used
to identify half of the victims.
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Bones and Teeth
In another case, a forensic dentist examined eleven of the
seventeen victims of Jeffrey Dahmer, a serial killer.
This was a particularly gruesome task because Dahmer
had disposed of the bodies by placing them in a 50 gallon
drum of muriatic acid.
The acid dissolved all of the tissues from the bones as
well as the roots of single rooted teeth.
What investigators found in and around Dahmers home
were stacks of bones, skulls, and loose teeth.
Dentists were able to place the loose teeth back into the
skulls from which they came, then match dental records
to the teeth.
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Dont Bite
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Adults
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Adults Children
8 incisors 8 incisors
4 canines 4 canines
8 premolars 8 deciduous molars
(sometimes called No premolars
bicuspids)
12 molars
95
Please note: When you look at the tooth chart, you are
looking into a person's mouth with the jaws open. You're
facing the person, so their upper right jaw will be on the left
of this image.
Teeth are numbered
from 1 32.
Start at upper right (1)
and count across to
upper left (16).
Then move down to
lower left (17) and
across to lower right
(32)
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Age
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Diet
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Different teeth have different purposes:
Incisors next to the front teeth and look
like chisels used to bite food.
Canines the sharp, pointed teeth next to
the incisors used to tear food.
Premolars uneven flat surfaces for grinding
and chewing food.
Molars uneven flat surfaces for grinding
and chewing food.
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Dental X-rays
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Radiograph
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Diagram that shows primary
(blue) and secondary (yellow)
teeth erupting
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2 years old
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5 years old
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8 years old
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107
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Ancestry
Generally, from skull appearance,
forensic dentists can determine
race within the three major
groups:
Caucasoid,
Mongoloid
Negroid.
Additional characteristics
such as shovel-shaped
incisors and multi-cusped
premolars, can also
assist in determination of
ancestry.
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Multi-cusped premolars can also
assist in determination of ancestry
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Sex