Firearms and Toolmark Identification.

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• Firearms and Toolmark Identification.
• Matching bullets to the gun that fired them.
• Identifying characteristics between tools, such
  as a pry bar, and the object on which it is used,
  such as a door frame.
• Explosives and imprint evidence.
• Forensic Psychiatry and Profiling.
• What creates mental illness and disorder,
• Diagnosis and treatment.
• Examine certain crime scenes to come up with a
  personality profile of the offender.  
• Questioned Document Examination.
• Special relationships that may exist between
  document and inscription and how it relates to a
  person or sequence of events.
• Includes forgery, counterfeiting, handwriting
  analysis and other related subdisciplines.
• Personal Identification.
• Fingerprints, dna analysis,
• Odontology, and a number of other subdisciplines.

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Firearms and Tool mark Identification.
Bullets are tested in the lab by test firing a
bullet through the suspect weapon.  The test
fired bullet is then compared under a comparison
microscope, side by side, to the bullet recovered
from the crime scene.  Both bullets are rotated
until the striations can be made to line up,
showing a match.  If the striations cannot be
lined up, the result is negative.
Certain parts of a firearm mark the bullet and
cartridge. When the gunpowder in the cartridge is
ignited, it forces the bullet down the gun
barrel, expanding the soft lead into the lands
and groves.  As the bullet passes down the
barrel, microscopic scratches from the lands and
grooves mark the bullet.  These microscopic
scratches are a by-product of the manufacturing
process and are totally unique to a particular
firearm.  
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Wheel base is the distance between the two front
wheels and the distance between the front and
rear wheels.  There are guys in labs who have
charted out these distances and can use this
chart to narrow down the make of the car.  The
tread design itself, as discussed above, can
narrow down the list of possible cars.  There are
books that contain images of every type of tire
imprint, just for this purpose.  The individual
wear developed from use will show up in the
impression, allowing for identification of a
single car, to the exclusion of all others. It
can also be deduced which way the car was facing,
how they pulled out and in what direction.  
There are three types of toolmark impressions
Compression, in which a tool surface presses into
a softer material Sliding, in which a tool
 (such as a screwdriver, below) scrapes across a
surface causing parallel striations and cutting,
which is a combination of the above two types (as
with scissors).  All three types can yield class
and individual characteristics.  In this way,
marks left on a doorway from a pry bar can be
matched back to that specific pry bar.
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Forensic Psychiatry and Profiling.
Profiling is a label given to the process by
which a trained forensic psychologist sifts
through the aspects of a crime scene to develop a
description of the personality of the
perpetrator. This personality description can
include age, sex, occupation, behavioral
disorders, upbringing, marital status, they type
of place the perpetrator would live in and its
general condition, the type of person the
perpetrator might live with, what type of car he
drives, if he has a speech impediment or acne or
some other type of disability or difficulty in
relating to others.  They will tell you how the
crime was committed.
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Questioned Document Examination.
The basic principle underlying handwriting
analysis is that no two people write the exact
same thing the exact same way.    Every person
develops unique peculiarities and characteristics
in their handwriting.   Handwriting analysis
looks at letter formations, connecting strokes
between the letters, upstrokes, retraces, down
strokes, spacing, baseline, curves, size,
distortions, hesitations and a number of other
characteristics of handwriting.  By examining
these details and variations in a questioned
sample and comparing them to a sample of known
authorship, a determination can be made as the
whether or not the authorship is genuine. 
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There are many ways to match a page back to a
photocopier or laser printer. The paper itself
can yield many clues.  Look for marks from the
belts, pinchers, rollers and gears that
physically move the paper through a machine.  
Toner can have unique characteristics in its
chemical composition.  Also, look at how the tone
was placed on and fused to the paper.  Toner may
clump up on the drum, tranfering blobs of toner
at a time to the printed page.   Marks on the
optics (glass platen, lenses, mirrors) used to
transfer or create an image on paper might
contain unique defects (such as scratches) that
will render anomalous markings on the printed
page.
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Personal Identification.
There are three basic fingerprint patterns
Loops, Arches and Whorls.  Everyone falls into
one of these three patterns (diagram).  Within
these patterns are what we call minutia points.
 There are about thirty different types of
minutae points, and no two people have the same
types of minutae in the same number in the same
places on their fingertips.  This is why our
fingerprints are totally unique.  
Your fingerprints are formed underneath your skin
in a layer called dermal papilae.  As long as
that layer of papilae is there, your fingerprints
will always come back, even after scarring or
burning.  
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Prints are left on a surface because we are
constantly secreting water and body oils and
other compounds through our pores.  This material
is left on the surface we touch in the form of a
fingerprint.   Different surfaces require
different techniques for developing prints.  In
the movies, you usually see detectives with
brushes.  They are powder processing the prints.
 Minute particles of powder cling to the print
residue as the brush passes over it.  The print
is then lifted with tape.  Another process
involves fuming.  Vapors of iodine and superglue
(bonds in seconds) will coalesce inside the print
residue to reveal a latent print.   There are
special processes that develop prints on paper,
wood and cardboard.  Fingerprints can be
developed on objects that have been in water.
 Prints can be developed off of skin (such as
from the neck of a strangulation victim).  There
are very few surfaces on which a print cannot be
developed.
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Gloves don't necessarily help you from leaving
fingerprints.  Surgical gloves were made to keep
surgeons from infecting their patients.  You can
actually leave prints through surgical gloves.
 Surgical gloves were made to keep sterile
conditions during operations.  They have to fit
like a second skin for surgeons to be able to
pick up their instruments. They fit so tightly
that fingerprints 'pass through' the latex
membrane.  They can also be turned inside out to
yield fingerprints from the inside surfaces.
 Leather gloves can be treated in the same
manner.  Also, leather gloves can leave a print
that is unique to that glove and no other
(leather comes from cow skin, which is just as
random as human skin).  Even cloth gloves, such
as mittens, can leave a distinctive print that
can be traced back to the mitten that made it.
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Forensic Anthropology seeks to identify remains,
such as bones.  From a skeleton, you can tell if
the subject is human, its sex, the age of the
subject when death occurred, stature, how long
the remains have been in their current state and
the cause of death.  
Hair Comparisons are another major component in
forensic science.  Hair can be determined to be
human or animal.  The body area from which a
questioned hair came can be identified.  Race can
sometimes be determined.  Disease conditions can
be determined. And, of course, a hair found at a
crime scene can be matched to the person that
left it there.  It's a relatively simple
comparison, involving side by side examination of
the suspect and known hairs, similar to bullet
matching.
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One DNA analysis technique looks at junk DNA.
 Everybodys' DNA is pretty similar.  Everyone who
has blue eyes has pretty much the same code for
blue eyes. Everyone who has brown hair has pretty
much the same code for brown hair.  But these
coding sequences are separated by 'junk' DNA.
 This 'junk' DNA is non-coding and only serves to
separate the coding sequences.  These 'junk' DNA
sequences are totally random and totally unique
to an individual.  The process is extremely
technical, but that is the concept, and it's
really not that hard to understand.  
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Do It Yourselves! You will need a zip lock bag, a
tube of superglue (the gel version works a little
better) and a can of soda or drinking glass.
  Place the can or glass in the zip lock bag.
 Lay the baggie flat on the counter.  Squeeze out
a generous amount of superglue into the bag
(don't glue the glass to the baggie).  Seal up
the bag.  If you can, blow some hot, moist air
into the baggie, like when you're trying to fog
up a window with your breath.  Seal it tight.
 The vapors from the superglue will build up in
the tiny zip lock atmosphere and creep up into
the prints on the glass or can.  There, they will
crystallize and, after awhile, you should see
starchy white fingerprints develop on the glass
or can.