Title: JS 112 Impression and Firearm examination
1JS 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
2Impression 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)
3Tire Impressions
- Tire Impressions plaster casts
- Photograph with lens perpendicular-why?
- Photograph with scale why?
4Shoe Impressions
- May be 3D as in soil
- Use flashlight for side-lighting
52D (two dimensional) on paper, floor, doors, etc.
6Shoe Impressions cont.
- Always photograph with scale
- Preservation techniques beyond photography
- Plaster Casts
- Tape Lifts
7Shoe Impressions In the Lab
- Lab Techniques
- Use photographs
- Copy test impressions onto transparency film
- Look for class and individual characteristics
8Case File Shoe Impressions in People v. O.J.
Simpson
9Comparison of Questioned Impressions (left and
center) to Known Bruno Magli Shoe (right)
10Shoe 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?
11Typical semi-automatic and revolver
12Bullets and Cartridge Case nomenclature
13The 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
14No 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.
15Test 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.
16Bullet 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
17Firearms 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.
18Anatomy of Shotguns-
19Shotguns 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
20Maximum range of common shot sizes
21Pattern of shot may be used to determine distance
22Cartridge 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
23Cartridge case markings
24IBIS- 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
25IBIS bullet case
26Gun 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
27Distance 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
28Powder 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
29Garments 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.
30Gunshot 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)
31Collection 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?
32Collection 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