Where is gunshot residue usually found

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					BALLISTICS
The big picture of ballistics

Because every contact leaves a trace (Locard’s
  exchange principle) very hard contacts (like a
  180 mps to 1500 mps contact) will leave a
  big trace
History of
Gunpowder and Firearms

 The Chinese invented gunpowder over a
    thousand years ago.
   Muzzle-loading matchlocks used wicks to
    ignite the gunpowder.
   The cartridge and breech loading followed.
   Rifling provided greater accuracy.
   Revolver, semi-automatic, and automatic
    handguns were developed.
 Ballistics
  –   The study of projectiles, trajectories,
      and the effect on the target
       Firearms Identification
         – A sub-discipline of ballistics that
           determining whether a bullet or
           cartridge was fired by a particular
           weapon
Introduction

Ballistic evidence helps explain:
 What type of firearm was used.
 The caliber of the bullet.
 The number of bullets fired.
 Where the shooter was.
 Whether a weapon was fired recently.
 If a firearm was used in previous crimes.
A    Internal ballistics
    What happens in the weapon

B     External ballistics
    What happens after the bullet leaves the
     barrel

C    Terminal ballistics (wound ballistics)
    What happens when the bullet hits the target
A Internal ballistics (1 of 3)


INTERNAL
 BALLISTICS
   SO WHAT’S A CARTRIDGE?
 a combination of:
 –   a projectile (the bullet)
 –   a propellant (gunpowder, for example)
 –   a primer (the explosive cap),




                                         A
          Cartridges Design




The bullet, usually made of metal, is out front
with the cartridge, holding the primer and
propellant powders, behind.
Watch this short video

   http://www.youtube.com/watch?v=c1VD1D1h
    LsQ
How a gun Works
1. The firing pin hits the base of the
   cartridge, igniting the primer powder.
2. The primer powder sparks through the
   flash hole to the main propellant supply.
3. The pressure of the explosion pushes
   the bullet from the case into the barrel.
4. The bullet follows the lands and grooves
   spiraling out of the barrel.
                     Land = high
   BACK OF BULLET
                     Groove = Low
ABROACH CUTTER USED
TO CREATE RIFFLING
IMPRESSIONS IN A
BARREL
As a result of rifling, a barrel will impress a
negative impression of itself on the sides of
the bullet like those seen below.




                                         A
 Matching
impressions




              A
      A fired bullet as class evidence

 Different gun manufacturers use different
 rifling techniques. These techniques
 impart the class characteristics on a fired
 bullet.
  –   Number of impressions
  –   Width of impressions
  –   Depth of impressions
  –   Angle of impressions
Q: How are these 2 guns different




     A: caliber
                                            A
What is caliber?
 Caliber = the diameter of the bullet.
 Measured in hundredths of an inches.
  –   .22,   .357, or .50
 Measured in metrics
  –   9mm
Question: Why should the caliber of ammunition
  match the firearm that shoots it? If they do not
  match, what could go wrong?
Showing variation within caliber
 INTERNAL BALISTICS (2 OF 3)

BREECH MARKS ARE
 FOUND ON THE
 REAR OF A FIRED
 CARTRIDGE
                               A
A
         Firing pin




Breech
A
   When a bullet is fired, the explosion forces:
    1. the bullet down barrel
    2. the cartridge back against breech
      –   Leaving a negative impression on the back of
          the cartridge
Depending   on the
make of gun & normal
wear and tear, the
breech markings will
pick up class, and
hopefully, individual
characteristics.
Examples of breech markings
How CSI determines if a recovered
bullet from a crime scene came
from a suspected gun
Disclaimer: this video is oooooold
   http://www.youtube.com/watch?v=3EJrbpg43
    qM
   Shotguns have smooth barrels with no rifling.
    –   Are there lands or groves on the bullet(s)?
   How can a F.S. identify trace evidence left by
    a shotgun?
    –   Only by marks on the spent shell casing(s):
Shotgun into ballistics gel
B
EXTERNAL
BALLISTICS
 External  ballistics is
 everything that happens after
 the bullet leaves the gun to just
 before the BULLET impacts its
 target
GUN SHOT RESIDUE
    GUN SHOT RESIDUE
    (GSR)



   CAN BE DETECTED
    EVEN AFTER WASHING
    CLOTHING / HANDS
  Gunshot Residues
 Particles of unburned powder and traces
  of smoke are the residues of gunshots.
 They can leave a trace on:
  – Shooter
      hand, arm, face, hair, or clothing
  – Victim
 Chemical testing often can detect residue
  even if removal is attempted.
 The distance from the victim to the
  shooter can be determined by
  examination of the residue pattern on the
  victim.
Trajectory
                         Wind shield




    Distance along path of                                   Path of bullet
    bullet to window, 23.9”


                                               x
                                                                    y


                                                   60 feet    Horizon

                              Distance along
                              horizon to
                              window, 23.5”
   Trajectory
 2 Reference points needed to
  determine trajectory
  – can be bullet holes in objects or victims.


 Investigators can use lasers to trace a
  straight-line path to help determine the
  position of the shooter.
http://www.glenbrook.k12.il.us/
http://www.glenbrook.k12.il.us/
External ballistics
                             Point of impact
Point of initial           Point of secondary
  intersection               intersection
                   Maximum ordinate




                                Point of aim
                     5 Ballistic Terms
   PII – Point of Initial Intersect. Where the bullet crosses the
    LOS (Line of Sight) for the first time.

   MO – Maximum Ordinate. The highest point the bullet
    reaches during its parabolic flight path.

   PSI – Point of Secondary Intersect. The point where the
    bullet crosses the LOS for the second time.

   POI – Point of Impact. The point where the bullet impacts the
    target.

   POA – Point of Aim. Where the shooter was aiming the
    weapon.
       If the sights are properly adjusted:
           POI = POA = DOA (dead on arrival)
C   Terminal ballistics
Bullet Wounds
1. Why do entrance wounds tend to be smaller than exit
   wounds?
2. If the bullet penetrates clothing, what can fibers
   embedded in the wound indicate?
3. Where is gunshot residue usually found?
4. If the gun is fired with the muzzle touching the victim’s
   skin, what telltale mark may show up?
5. Will larger or will smaller caliber bullets tend to lodge
   within the body rather than passing through? Why?
GUN SHOT RESIDUE
Bullet wounds (4 kinds)

 1.   Barrel on skin
 2.   Barrel just off skin
 3.   Barrel inches away
 4.   Shot from a distance
Barrel on skin
           Notice:
           Distinctive star pattern, so…

                 energy from the gun shot
                 forced back out entryway
                 “blowback”

           NO burnt gun powder marks
           around entryway, so…

              •ALL gunpowder delivered
              inside entryway singing the
              interior (black area)
        Barrel inches away
 Notice:
 “stippling” of
  the burning
  powder around
  the actual
  bullet entry way
 No star pattern
    –   No “blow back”
Barrel just off skin
        Notice:
         - no star pattern so..
            –   not ON skin
           No stippling from g.p. so..
            –   TOO close for inches away
           Barrel burns like on skin
            so….
            –   JUST off skin
 9mm   to person’s back NOTICE:
 – Lack of burnt gun powder burns on skin
 – Lack of star pattern




Conclusion = shot from distance
(probably through clothes)
THE END
Shot from distance
(but photo shopped)

				
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