Impression Evidence• Just like fingerprints and palmprints
– Looking for similarities and differences
• Class and Individual Characteristics– Class is shared by like items
• It’s a size 9 Reebok Perimeter
– Individual is unique to individual evidence• It’s this size 9 Reebok Perimeter
Shoe Print Case• Respond to Woonsocket Plaza for Larceny of Copper• Find Shoeprints on the Black Tar Rubberized Roof near
the Air Conditioning Units• Follow prints to edge of building finding point of entry• Send shoeprints to FBI (maintain a database of shoe
impressions)• FBI identifies shoe as a Reebok Perimeter
Four Components of Ammunition
• Primer
– Rimmed or Centerfire
• Cartridge Case or Shotshell
• Propellant
• Projectile(s)
• When a firearm is manufactured, the individual parts are made with tools that are in a constant state of change
• As a result, no two guns will leave the same marks on the ammunition components
• The marks found on bullets are sometimes referred to as striations
Source of Gunshot Residue
• Firing a weapon may cause microscopic particles of primer residue and gunpowder to be deposited on the hands of the shooter
• The higher the caliber, the more GSR depositied on hands
• .22 caliber rim-fire cartridges will sometimes not show traditional GSR particles
Primers
• Lead Styphnate– Primary explosive
• Barium Nitrate– Oxygen Source
• Antimony Sulfide– Fuel
Formation of the Particle
• Upon detonation, the compounds of the primer vaporize, mix and then condense back into particles
• The result: what was once three separate particles have become one particle made up of lead, barium and antimony
Inside a GSR kit
• Each GSR kit contains– Instructions– A pair of rubber gloves– Labels– Two sample vials
• Each vial contains adhesive coated aluminum stub mounted on the base of a rubber stopper
• Stub pressed and lifted on the surface being sampled– Hand – Face– Clothing
The Examination
• Look for particles with the proper morphology and size
• Look for particles which contain all three components of the primer– Lead (Pb)– Barium (Ba)– Antimony (Sb)
Positive: What does it mean?
• The individual fired a weapon
• The individual handled a weapon right after it was fired
• The individual was very near when the gun was fired
• The individual touched a surface that had GSR on it.
• Etc, etc, etc.
Negative: What does it mean?
• The individual did not fire a weapon
• The individual washed their hands
• The sample was collected after the recommended 4-6 hour time window
• The individual was wearing gloves when they fired the weapon
• Etc, etc, etc.
Projectile Penetration
• Three Possibilities– Projectile is stopped by impact without
penetration– Projectile will penetrate the object without
exiting– Projectile will pass through object (Perforate)
Definitions
• PenetrationPenetration is when a projectile enters but does
not exit. Not to be confused with Perforation
• Perforation Perforation is when a projectile passes through
and through. Not to be confused with Penetration
Shotgun Pellet PatternsIn General…. For every 1” across
= 1 Yard from Muzzle
7”
Muzzle to Target = 7 Yards
450 Incident Angle with No. 4 Buck, 12 ga.
d = 7 in.
d/D = 0.67Sin-1 = 420
Same Rangeas previous shot
Everything from MidtermPlusBallisticsAmmo componentsChemicalsRiflingStriationsGSRWhat it meansTrajectoryPenetrationPerforationShotgun
1” for 1 yardCasingsGlass – 2 shots which one firstDifference between class and individual characteristics
Blood SpatterDefinitionsFormulaLVISMVISHVISTests
EyewitnessPolygraph3 measurementsPhysiological changesHeart RespirationPerspirationReactionEyesCotton mouthButterflies