JS 96GY Impression and Firearm examination

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JS 96GY- Impression and Firearm examination

• Announcements and Assignments
• a. Read Chapters 7 and 11
• b. Impression exercise Monday (shoeprints)
• 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
• Print Screen with your results
• Impression Evidence
• Firearms
• Acknowledgements Ms. Marty Blake (SFPD), Lucian
  Haag, Ron Nichols

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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)

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Tire Impressions

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

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Shoe Impressions

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

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2D (two dimensional) on paper, floor, doors, etc.
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Shoe Impressions cont.

• Always photograph with scale
• Preservation techniques beyond photography
• Plaster Casts
• Tape Lifts

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Shoe Impressions In the Lab

• Lab Techniques
• Use photographs
• Copy test impressions onto transparency film
• Look for class and individual characteristics

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Case File Shoe Impressions in People v. O.J.
Simpson
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Comparison of Questioned Impressions (left and
center) to Known Bruno Magli Shoe (right)
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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?

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Typical semi-automatic and revolver
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Bullets and Cartridge Case nomenclature
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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

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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.

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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.

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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

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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.

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Anatomy of Shotguns-
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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

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Maximum range of common shot sizes
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Pattern of shot may be used to determine distance
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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

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Cartridge case markings
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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
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IBIS bullet case
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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

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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

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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

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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.

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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)

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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?

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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