Forensic Science

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Forensic Science

• By Jessica Kershaw

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Contents

• Slide 19 paint
• Slide 20 rope, twine, cord
• Slide 21 smoking materials
• Slide 22 series
• Slide 23 try this at home
• Slide 24 hair comparisons
• Slide 25 bullet matching
• Slide 26 bullet matching (continued)
• Slide 27 bullet matching (continued 2)
• Slide 28 imprint evidence
• Slide 29 imprint evidence (continued)
• Slide 30 imprints evidence (continued 2)
• Slide 31 imprints (continued 2)

• Slide 3 - fingerprints
• Slide 4 - finger prints (continued)
• Slide 5
• Slide 6 - trace evidence
• Slide 7 - trace evidence (continued)
• Slide 8 - DNA
• Slide 9 - DNA (continued)
• Slide 10 - DNA (continued 2)
• Slide 11 facial reconstruction
• Slide 12 blood spatter
• Slide 13 blood spatter (continued)
• Slide 14 cast off stains
• Slide 15 soil trace
• Slide 16 fracture match
• Slide 17 glass
• Slide 18 glass (continued)

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Finger Prints

• To identify the three patterns, note the 'delta',
  the point where lines from three directions come
  together. The whorl has two deltas, the loop has
  one (see bottom-left), and the arch has no delta
  at all.
• To see if you have a rare fingerprint, check
  which finger it is found on. For example, a
  radial loop is common on the index finger, but
  extremely rare on the little finger.

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Finger prints (continued)
Double loop

• Fingerprints are one of the best forms of
  physical evidence. A fingerprint can conclusively
  identify both offenders and victims. State wide,
  and soon, nation wide databases are available for
  rapid computerized searching. There are a number
  of methods of processing for fingerprints.

Peacocks eye
Tented arch
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Finger prints (continued 2)

• 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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Trace evidence

• Criminals always take something away from the
  scene of the crime, it might be the dirt on there
  shoes or it could be a victims hair on there
  clothes. Also criminals almost always leave
  something behind at the scene it could just be a
  scrap of fabric a stand of hair or even a drop of
  sweat, all of witch can be used as evidence!

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Trace evidence (continued)

• Criminalistics and Trace Evidence are both terms
  that apply to all types of physical evidence that
  may be circumstantial evidence in the trial of a
  case. Most often, the term is meant to include a
  variety of types of trace evidence analysed by
  experts who are sometimes identified as "micro
  analysts,".

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DNA

• DNA is constructed like a ladder a ladder that
  has been grabbed at both ends and twisted,
  creating the double helix shape.  The rails of
  the ladder are phosphate and sugar groups. They
  link together to form the backbone.  

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DNA (continued)

•  Everybody's 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.  

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DNA (continued 2)

•  The examining labs have samples of DNA, taken
  from a representative population group.  These
  are entered into a database, to which the
  questioned DNA (that being compared for analysis
  in a case) is compared for frequency among the
  population group.  That is DNA testing at its
  most basic.  

11
Facial reconstruction

•  The photo imposition technique involves
  imposing a photo of the skull over a photo of the
  face in question.  This is examined in the
  Romanov book in the 'suggested reading' link.
   Three dimensional reconstruction
  technique involves adding depth markers for
  tissue thickness onto a skull.  The depths are an
  average taken from cadavers.  Clay is placed over
  the skull, to match the depth of the markers, to
  simulate skin and muscle.  The features are then
  smoothed out to make a 'face.'  This has worked
  in a number of missing persons cases, but is
  considered more art than science.  

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Blood spatter

• Blood spatters help a great deal in
  reconstructing a crime scene.  They can be used
  to corroborate or disprove and alibi.  They can
  be used to convict the guilty.  There is much
  more to it than looking at a stain or spatter and
  saying, "This is where the crime took place."
   The patterns of the spatters and the shapes of
  the individual blood droplets themselves can tell
  how the crime was committed.

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Blood spatter (continued)

• Drops falling from different heights (i.e. at
  different speeds) will leave different looking
  spatters.  A drop falling from a low height of a
  few inches will leave a small cohesive circle.
   At greater heights, the circle will be larger
  and may even have a 'crown' effect.
• Hitting a surface at an angle does even more to
  disrupt a blood droplet.  Perpendicular impact
  leaves a droplet fairly uniform, as shown below.
   A droplet hitting a surface at an angle will
  bulge out in one direction, indicating the
  direction of travel of the droplet.  

14
Cast off stains

• Cast off stains are a result of  blunt force
  trauma (beating with an object such as a hammer).
   Pulling back from a blow produces a blood
  spatter that indicates direction, by creating an
  arc of blood droplets.  You can determine the
  number of blows inflicted by counting the arcs.
   You can also determine the orientation of the
  individuals involved, the size of the object used
  and the right or left handedness of the
  assailant.  

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Soil trace

• Soil can be used to associate a particular scene
  with a a particular individual.  Typical
  collection sites include shoes, tires, pedals,
  carpeting and wheel wells on cars.  Soil can also
  be used to determine if an individual has been
  moved.  Soil characteristics vary with geographic
  location.  If soil on the body doesn't match the
  composition of the soil where it was found, the
  body was obviously moved.  Also, soil found out
  of its native geographical area can be matched
  back to its area of origination.

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Fracture match

• The fracture match is another important concept,
  particularly when trace evidence is concerned.
   Tear a piece of paper in half.  Hold the two
  halves together.  This is called a fracture
  match. No two tears are exactly alike.  One half
  of a tear can always be matched back to its other
  half.  Remember that.  If a half of something
  found at a crime scene can be matched to the
  other half of something found on a suspect,
  that's damn good physical evidence.

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Glass

• Glass breaks in a characteristic manner which
  indicates the direction of travel of the
  impacting object.  Conchoidial striations are
  ripples seen through the cross section of broken
  glass. They are always at right angles to the
  impacted surface.  

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Glass (continued)

• Class characteristics of glass include its
  colour, thickness and refractive index (how much
  it bends the light that passes through it), and
  whether it is flat or curved. Individual
  characteristics include fingerprints, fracture
  matches, saliva or lip prints (if it is a
  drinking glass or someone has pressed their face
  against a window), blood and prints from nose,
  tongue, chin or mouth.  There may be a drug or
  liquid residue on the glass or even footprints if
  the glass if found on the floor.  

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Paint

• Paint can be examined and matched for color and
  texture.  Also, a paint chip can be fracture
  matched back to the point from which it
  originated.  Also, if several layers of paint
  have been applied over one another, a stronger
  match can be made.  What are the chances that
  some one else used the exact same colors of paint
  in the exact same sequence?

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Rope , Twine , Cord

• In the event of death by hanging, skin tissue on
  the fixed side of the rope can indicate homicide
  rather than suicide.  Never cut a noose or alter
  the knot.  There is the possibility of a fracture
  match if the length of rope found at the scene
  was cut from a larger length of rope.  The rope
  or cord may have die marks or striations from the
  manufacturing process that can be used to
  identify its manufacturer.  Also, fingerprints
  might be resolved from smoother cords.  

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Smoking materials

• Ashes from cigars, pipes and cigarettes can be
  differentiated.  Also, butts can have saliva, lip
  prints, fingerprints, blood stains and bite
  marks.  
• Matches can be fracture matched back to the book
  from which they were torn.  Matchbook covers can
  reveal handwritten phone numbers and names, and
  are usually printed with a logo or other
  information that can identify a unique location.
   Fingerprints can be developed from matches and
  matchbooks.  

22
A Series

• Trash bags come out of the box in a strip.  They
  are separated by a line of notches / perforations
  running perpendicular to the open end.  These
  perforations make for an easy tear and connect
  one bag to the next bag in the box.  Each
  individual perforation at the bottom of a trash
  bag is a tiny little fracture match one half
  from the bag you just tore off, the other half
  from the next bag in sequence that is still in
  the box. In this way, using the perforations as
  little fracture matches, a series of trash bags
  from the same box can be placed in their proper
  sequence, as they were torn off the roll in the
  box.  

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Try this at home!

• Try this at home  You will need a zip lock
  sandwich bag, a tube of superglue (gel version
  works better) and a can of pop or drinking glass.
   Place the can or glass in the zip lock sandwich
  bag.  Lay the sandwich bag flat on the table.
   Squeeze out a generous amount of superglue into
  the sandwich bag (don't glue the glass to the
  sandwich bag).  Seal up the sandwich bag.  If you
  can, blow some hot, moist air into the sandwich
  bag, like when you're trying to fog up a window
  with your breath.  Seal it tight.  The vapours
  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.  

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Hair comparisons

• Hair Comparisons are another biggie 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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Bullet matching

• Certain parts of a firearm mark the bullet and
  cartridge.  Rifling gives the bullet a signature
  marking that is unique to the weapon that fired
  it.  Rifling exists as part of the manufacturing
  process of the firearm and serves to put spin on
  the bullet, giving it a straighter trajectory
  (much the same way a quarterback puts spin on a
  football).  Rifling consists of lands and groves
  that spiral down the gun barrel (think of the
  seam on a paper towel tube).  

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Bullet matching (continued)

• 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.  Thus,
  the scratch marks on the bullet match the scratch
  marks in the barrel of the gun that fired it, to
  the exclusion of all other weapons.  

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Bullet matching (continued 2)

• This is 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.

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Imprint evidence

• There are two basic types of imprint evidence
   Three dimensional impressions, in which an
  object presses into something soft which retains
  the impression of that object and two
  dimensional impressions, in which an object
  transfers an image to a surface or an object
  comes into contact with a surface that is coated
  and removes some of that coating.  
• An example of a 3d impression is something
  stepping into mud.  You've all seen Big Foot
  documentaries where a camper finds a huge foot
  print out in the woods.  This is a 3d print.  Big
  Foot (for lack of a better explanation) has
  stepped in the mud and left a foot print behind.
  The mud hardens as it dries and retains the
  print.

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Imprint evidence

• Tire impressions can be extremely useful.  Let's
  say there is a bank robbery.  The perpetrators
  parked behind the bank (as per the diagram
  below).  As the fled, they unknowingly left
  behind a bunch of clues. Wheel base is the
  distance between the two front wheels and the
  distance between the front and rear wheels.   

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Imprints (continued)

• 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. We can also tell which way the car
  was facing, how they pulled out and in what
  direction.  

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Imprint evidence (continued 2)

• An example of the first type of 2d print would be
  the step after you've stepped into spilled paint.
   The paint coats the bottom of your shoe when you
  step in it.  It is then transferred to another
  surface when you step down.  It is just like
  using a rubber ink stamp.  

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I hope you have enjoyed my presentation
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The end