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JS 112 Impression and Firearm examination

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d. Visit www.firearmsid.com: See Virtual Comparison scope ... Remaining original bore is called lands. Diameter of the bore is the caliber ... – PowerPoint PPT presentation

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Title: JS 112 Impression and Firearm examination


1
JS 112- Impression and Firearm examination
  • Announcements and Assignments
  • a. Quiz
  • b. Crime Scene exercise- Weds Shoeprints
  • c. Read Chapters 11 and 12
  • d. Visit www.firearmsid.com See Virtual
    Comparison scope
  • and/or shoeprint database site
    http//www.xtek.net/catalogue/forensic/sicar.shtml
  • 1 point extra credit for summarizing site-
    overview of pages and information in 500 words
  • 1 point extra credit for each match verified
    - Due Monday 22 October
  • Print Screen with your results
  • Impression Evidence Shoeprint exercise
  • Firearms

2
Impression Evidence
  • Something harder contacts something softer, or
  • Transfer of material like blood
  • May be 2D or 3D
  • Includes fingerprints, toolmarks, firing pin,
    shoe, tire, fabric (hit and run)

3
Tire Impressions
  • Tire Impressions plaster casts
  • Photograph with lens perpendicular-why?
  • Photograph with scale why?

4
Shoe Impressions
  • May be 3D as in soil
  • Use flashlight for side-lighting

5
2D (two dimensional) on paper, floor, doors, etc.
6
Shoe Impressions cont.
  • Always photograph with scale
  • Preservation techniques beyond photography
  • Plaster Casts
  • Tape Lifts

7
Shoe Impressions In the Lab
  • Lab Techniques
  • Use photographs
  • Copy test impressions onto transparency film
  • Look for class and individual characteristics

8
Case File Shoe Impressions in People v. O.J.
Simpson
9
Comparison of Questioned Impressions (left and
center) to Known Bruno Magli Shoe (right)
10
Shoe Impression exercises
  • Teammate shoe class vs individual characteristics
  • Identify class characteristics
  • Identify any individual characteristics
  • Document your shoe with a list of each of these
    characteristics and sketch
  • Compare exemplar shoes to impression casts 1-6.
  • Can you identify any exclusions?
  • Any inclusions? Why or why not?

11
Typical semi-automatic and revolver
12
Bullets and Cartridge Case nomenclature
13
The inner surface of the barrel of the gun leaves
markings on a bullet passing through
  • Markings or inner surface striations are unique
    to each gun.
  • Bullet at crime scene markings are the same on
    one test fired from a suspects gun ? link to
    crime
  • Gun barrels made by drilling solid steel bars
  • Spiral grooves called rifling are also added
    imparting rapid spins
  • Remaining original bore is called lands
  • Diameter of the bore is the caliber

14
No two rifled barrels, even those manufactured in
succession, will have identical striation
markings!
  • Smith and Wesson 0.32 caliber revolvers have five
    lands and grooves with same approximate width and
    twist to the right.
  • Colt 0.32 caliber revolvers have 6 lands and
    grooves to the left.
  • Individual characterstics are imparted from
    striations impressed into the metal as negatives
    of minute imperfections found on the rifling
    cutters tools.
  • As the bullet passes through its surface is
    impressed with these rifling marks.

15
Test firings are required to compare markings of
the barrel to those left on the bullet
  • Class and individual characteristics of the
    barrel will be imparted to the bullets fired
    through a barrel.
  • Test bullets are compared to those found at the
    crime for matching class characteristics and then
    matching striation markings using a comparison
    microscope.

16
Bullet examinations
  • Class characteristics -Number, width and
    direction of lands and grooves
  • Comparison of base to base to determine
  • More than one weapon
  • Same caliber different brand, fired from same
    weapon
  • Determine land and groove count on badly damaged
    bullet

17
Firearms examinations
  • Rarely finds perfect matches
  • Grit and rust alter markings
  • Mutilation of bullets on impact leaving only
    partial info
  • Striations are not permanent and subject to
    change and alteration through wear
  • Luckily changes are not dramatic
  • No hard and fast rule governing minimum number of
    points of comparison.
  • Final opinion based on judgement, experience and
    knowledge of the expert.

18
Anatomy of Shotguns-
19
Shotguns have smooth barrels
  • Shot guns fire small lead balls or pellets within
    the shell.
  • Paper or plastic wad pushes the pellet thought
    the barrel upon ignition of cartridge powder
  • Weighing and measuring the diameter of the shot
    recovered at the crime scene the examiner can
    determine size of shot and may reveal information
    on gauge- the diameter of the shotgun barrel or
    choke

20
Maximum range of common shot sizes
21
Pattern of shot may be used to determine distance
22
Cartridge cases are impressed by the firing pin
and breechblock
  • Pull trigger? firing pin strikes primer? ignites
    powder? gases and burning powder propel the
    bullet through the barrel? shell is impressed
    with markings by contact with metal surface of
    the weapons firing and loading mechanisms
  • Reproduce the markings with test fired cartridges
  • Firing pins impress the soft metal of the primer
    on the cartridge case reveal minute distortions
    of the pin
  • Cartridge case is impressed by its rearward
    thrust against the breechblock having random
    striations too.
  • Other distinctive markings may be left by
    ejectors, extractors and magazine clips

23
Cartridge case markings
24
IBIS- Integrated Ballistic Identification System
Drugfire- FBI cartridge cases IBIS
ATF-cartridge cases and bullets
incompatible 1999- NIBIN National Integrated
Ballistic Information Network Unified system with
both DRUGFIRE AND IBIS 800,000 images more than
8,000 matches in over 16,000 cases
25
IBIS bullet case
26
Gun powder residue and distance determinations
  • Ammunition is propelled by expanding gases
    produced by ignition of powder. Not all powder
    is burned.
  • Unburned and partially burned powder in addition
    to smoke are propelled out of the barrel along
    with the bullet toward the target
  • If the weapon is close, products will be
    deposited onto the target.
  • The distribution of gunpowder residue and other
    residues permits assessment of distance

27
Distance determination using Gunpowder residue
  • ZONE I-. CONTACT Blast destruction, tearing of
    the skin or cloth soot and powder particles
    mostly on the inside of the garment and/or driven
    into the' wound. The outline of certain parts of
    the firearm (e.g.- barrel bushing, front
    sight)may be printed in the skin adjacent to the
    entrv hole.
  • ZONE II NEAR-CONTACT ca. 1-4 inches) Intense,
    dark sooting with dense deposits of unburned and
    partially burned powder particles around the
    bullet hole blast destruction still possible in
    clothing and even skin in some cases powder
    tatooing on the skin.
  • ZONE III ca. 3-6 Inches Some medium to light
    gray sooting with a roughly circular "shotgun"
    pattern or distribution of powder particles
    around the bullet hole. Powder tatooing still
    possible particularly with dense and/or 'poorly
    burning powders.
  • ZONE IV ca. 6-24 Inches - No visible sooting
    widely dispersed powder particles often loosely
    adhering to the receiving surface distribution
    pattern is usually circular at closer distances
    but may become poorly defined to nonexistant at
    greater distances. Chemical tests can be employed
    to raise latent powder or GSR patterns on
    garments.
  • ZONE V ca. 3-4 Feet or Greater No discernable
    firearms discharge products present bullet
    wiping present around the margin of the entry
    side of the bullet hole regardless of range

28
Powder residue patterns from victims clothing
against patterns from test firing at various
distances
  • Similarity in shape and density of the residue
    pattern
  • Contact shots have heavy concentration of smoke
    like vaporous lead that surrounds the bullet
    entrance hole

29
Garments examined for gunpowder residue
  • Color, shape and size
  • IR photographs help to enhance contrast revealing
    vaporous lead and powder.
  • Greiss test- nitrite particle test using
    chemically treated gelatin coated photographic
    paper.

30
Gunshot residue also deposits on the hand of the
shooter
  • Dermal nitrite test first used
  • Hot wax or parrafin to hand of suspect? dried and
    treated with diphenylamine? blue
  • presence of nitrates
  • Non specific- fertilizaers, cosmetics and urine,
    and tobacco give falst positives
  • Lead styphnate, barium nitrate, and antimony
    sulfide on thumb web and vack of firing hand
  • Measure barium and antimony on relavant portions
    of the suspects hands adhesive tape of swab
  • Neutron activation analysis and atomic absorption
    spec used
  • Also SEM as elements have characteristic shape
    and size (7-12)

31
Collection and Preservation of Firearm evidence
  • Safety first Unload but
  • record hammer and safety position and location of
    all fired and unfired ammo in weapon
  • Chamber position in line with barrel indicated by
    mark on cylinder
  • Each chamber designated with a number and as each
    cartridge or case is removed it should be marked
    to correspond to numbered chambers.
  • Knowledge of cylinder position of casing
  • Each round in separate box or envelope
  • Magazine removed and checked for prints
  • Dont pick up with a pencil- disturbs powder
    deposits, rust or dirt in barrel altering
    striation markins on test-fired bullets
  • Recovery of latents? -hold by edge of the trigger
    guard or by checkered portion of the grip
  • Chain of custody, tag items with identifying data
  • If from underwater do not dry-keep submerged and
    submit to lab. Why?

32
Collection and Preservation of Ammunition
  • Preserve striations on bullets and casings
  • Free bullets by carefully breaking away
    surrounding support material
  • Scribe bullets with initial on the base or nose
  • If deformed place in container
  • Wrap in tissue paper before placing in box
  • Leave trace intact
  • Never mark near where firing pin strikes
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