Firearms and Toolmarks - CSI

What examinations are performed in the field of firearms and toolmarks?

-Firearms and ammo examined for identification and operability

-Expended ammo tested for identification and comparison

-Victim’s clothing examined to establish victim to muzzle distances

-Tools and toolmarks examined for comparison

-Shooting crime scene reconstruction

What actually is a firearm?

Any tube that uses an explosive charge to hurl a projectile. A weapon that doesn’t use an explosive charge but a mechanical delivery system is NOT a firearm (slingshot, crossbow, airgun, etc.)

What is the cartridge?

Unfired ammo that consists of the bullet, case, primer, and powder

What does a shotshell contain?

Tubing, brass head, powder, wad, filler, shot.

What are the main firearm safety tips?

-Treat every weapon as if its loaded at all times

-Always point weapon in a safe direction

-Keep finger off the trigger

What exactly happens when the trigger gets pulled?

-Firing pin or hammer strikes primer

-Primer ignites, igniting the powder

-Powder burns and creates gas pressure

-Bullet forced out and shot out the barrel by pressure

What are the types of handguns?

-Pistols

-Revolvers

What are the characteristics of a pistol?

-Cartridge in magazine or chamber

-Casings usually ejected and found at scenes

What are the characteristics of a revolver?

-Cartridges in cylinder

-Casings usually not ejected and usually not found at scenes

-Action must be opened and expended casings manually removed

What are long-guns?

-Designed to be shoulder-fired

-Rifles or shotguns

What’s the difference between rifles and shotguns?

Rifles: Cartridge and rifled bore

Shotguns: Shotshell and smooth bore

What are the five action types of rifles?

-Lever action

-Bolt action

-Hinged frame (action must be opened and expended shotshells

manually removed from firearm)

-Pump action

-Semi and full automatics

What is rifling and what are the types?

The spiral cuts in the barrel of a firearm that forms the lands and grooves, which increase accuracy, velocity, and stability. Types are right hand twist: clockwise, and left hand twist: counterclockwise

What is bullet jacketing and the types?

When a lead bullet is covered in another metal to improve its strength

-No jacket

-Semi-jacketed (only tip of bullet exposed)

-Full metal jacket (only bottom exposed)

-Total metal jacket (entire bullet covered)

What is the Black Talon?

-Hollow point projectile that flattens out. Segments peel back and form sharp “talons”

What are the class characteristics for expended bullets?

-Caliber/weight

-# of lands and grooves

-Direction and degree of twists

-Land impression width

-Groove impression width

How can you individualize expended bullets?

-Striation patterns in the land impressions

-Striation patterns in the groove impressions

What does the caliber of the bullet mean?

-The measurement of the base of the bullet

-Can be expressed as inches or millimeters (ex. .45 caliber = .45 inches or 9mm = 9millimeter)

What makes a shotguns caliber special?

They use the term “gauge.” Number of balls of lead per pound ex. 16 gauge.

What is shot based on for shotguns?

Size and number of pellets. Bird shot v buckshot.

What are the class characteristics of expended casings?

-Caliber

-Shape of firing chamber

-Firing pin shape/size and location

-Size of ejectors and extractors

-Geometrical relationship of ejectors and extractors

What are the individual characteristics of expended casings?

-Firing pin impression

-Breech block markings

-Extractor and ejector markings

What is IBIS? (Integrated Ballistics Identification System)

-Firearms related evidence database

-Sorts candidates by breechface correlation scores and firing pin correlation scores

-Cartridge character and firing pin shape class characteristics used to reduce candidates

What is gunshot residue?

-Particles from existing barrel residues

-Particles from bullet (lead, lead alloys, unburned and partially burned smokeless powder)

-Particles from primer (barium, antimony and lead)

How is distance from muzzle to target determined?

-Visual/Macroscopic examination

-Chemical tests for GSR (nitrates, lead, copper)

What can be determined through visual/macroscopic examination?

-Ripping/tearing and charring/melting of fibers or singeing of hair

-Presence of carbon soot

-Presence of unburned/partially burned powder particles

-Presence of bullet wipe (combustion products, bullet lubricant)

What is a Modified Greiss Test?

Chemical test used to determine presence of nitrite compounds, enhancing visibility of powder particle pattern (turns red)

What is a Sodium Rhodizonate Test?

Chemical test used to determine the presence of lead (vaporous, particulate, and wiped). (turns purple)

What is a Dithioximide test?

Chemical test used to detect the presence of copper which can be deposited in some bullet wipes

What are the characteristics of a near-contact wound? Also, should you wash them?

Grey ring of smoke around charred margins of skin. Don’t wash before inspection as GSR can be easily wiped off

What are the characteristics of exit wounds?

-Stellate defect instead of round entrance wound

-No foreign particles or stippling

-Usually larger than entrance wounds

-No bullet wipe

What should be done to firearm evidence on the scene?

-Record info (make, model, serial # if possible)

-Make it safe immediately

-Photograph potential bullet holes before searching

-Remove section of wall if bullet holes are present if needed

-Dont handle with metal forceps/tweezers

What are the steps of weapon and ammunition recovery?

-Recover firearm in a safe manner

-Document firearm and ammo

-Collect trace evidence, trace DNA and latent prints from firearm and ammo prior to firearm exams

-Properly package and seal evidence

How do you properly unload firearms (not revolvers)?

-Always remove ammo magazine first

-Open action and ensure chamber is empty

-Strap action open to make sure it can’t be used

How do you properly unload a revolver?

-Mark cylinder to indicate chamber under hammer

-Unload each chamber in cylinder, noting location

-Place each cartridge/casing in separate container

How should firearm evidence be packaged?

-Ammo in paper, plastic, or cardboard containers

-Firearms secured in box

What trace DNA can be found on firearm evidence?

-Suspect skin cells may be transferred onto coarse surfaces

-Latent fingerprints may be found on smooth surfaces