Impression Evidence

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

Firearms and Ballistics

How a gun works

Four Components of Ammunition

• Primer

– Rimmed or Centerfire

• Cartridge Case or Shotshell

• Propellant

• Projectile(s)

Ammunition

Ammunition

PREMIUM LOAD with SHOTCUP

Pellets do notcontact bore

Some problems

Stable vs. Instable

Projectile Flight

Rifling

• 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

The match on the bullet

Gunshot Residue

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.

Bullet Trajectory

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

Pellet Pattern Diameter vs. Range

Orthogonal Impacts

d d d

Non-Orthogonal Pellet Patterns

sin-1 (d/D) = incidence angle

Orthogonal StrikesNo. 4 Buck12-ga.

d = 7 in.

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