Firearms and Tool Mark Analysis

What are some examples of examinations performed?

1) Firearms and ammunition examined for identification and operability

2) Expended ammunition components tested for identification and comparison puzzles

3) Victims clothing tested to establish muzzle to victim distances.

4) Many forms of Tools & Toolmarks tested for comparison purposes.

5) Shooting Crime Scene Reconstruction.

What is a firearm?

Any tube that uses an explosive charge to hurl a projectile.

Are slingshots, crossbows, and air-guns firearms?

No

The cartridge

The case; the "unfired" ammunition

What is in a cartridge?

Bullet, case, powder, primer

The shotshell

Ammunition used in modern shotguns; a case containing primer, gunpowder, wad, and a slug or shot

What is in a shotshell?

(top to bottom) The case, the shot, the wad, the powder charge, and the brass head primer.

Firearm Safety

1) Treat every weapon as if it was loaded at all times

2) Always keep the weapon pointed in a safe direction

3) Keep your finger off the trigger

What happens when the trigger is pulled?

1) The firing pin or hammer strikes the primer/

2) The primer ignites, which in turn ignites the powder.

3) The propellant powers burns and creates gas pressure.

4) The bullet is forced out of the cartridge and moves down the barrel of the gun.

Who parented the first rifle?

Samuel Colt

What are examples of handguns?

Revolvers, pistols

Pistols

1) Cartridges are in magazines or chambers.

2) Casings are usually ejected and found at the scene.

Revolvers

1) Cartridges are in cylinders.

2) Casings are NOT ejected.

What are examples of long guns?

1) Designed to be shoulder fired.

2) Classifies as either rifles or shotguns.

Rifles

1) Has cartridges.

2) Rifled bore.

Shotguns

1) Has shotshells.

2) Usually smooth bore

What are the five action types of rifles and shotguns?

1) Lever action

2) Bolt action

3) Hinged frame

4) Pump action

5) Automatic

Rifling

Refers to the spiral cuts in the barrel of a gun that form the lands and grooves.

What are the two types of rifling?

Right hand twist(clockwise) and Left hand twist(counter-clockwise)

Bullet jacketing

Bullets are often jacketed, or covered with another metal(since bullets are made of lead).

What are the different types of bullet jacketing?

1) No jacket

2) Semi-jacket

3) Full metal jacket

4) Total metal jacket

Black talon

Defined as the projectile flattening out, or "mushrooming"

The segments peel back, creating numerous sharp points.

expended bullets

Caliber

The measurement of the base of the bullet-- can be expressed in inches or mm.

What do shotguns use in place of caliber?

Gauge-- for example, 16 gauge

gauge

The number of "balls of lead" of size equal to one pound.

What is the relationship between gauge and a barrel's diameter?

The higher the gauge, the smaller the barrel's diameter.

Integrated Ballistic Identification System (IBIS)

A database of digital images showing the identifying features of bullets and casings.

Gunshot residue

Particles from existing barrel residues, the bullet(lead, lead alloys) and primer(lead, barium, antimony)

Distance determination(Muzzle to target)

1) Visual/Macroscope examination

2) Chemical tests for gunshot residue (Nitrites, Lead, Copper)

Modified Greiss Test

Chemical test used to determine presence of nitrite compounds enhancing the visibility of the powder particle pattern

Dithioximide Test

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

Sodium Rhodizonate Test

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

Exit wound

1) Stellate defect as opposed to round entrance wound.

2) No foreign particles/stippling

3) No bullet wipe

4) Usually larger than entry

Bullet wipe

A gray or black ring around an entrance bullet hole

How should you record firearm evidence at a scene?

1) Record firearm info: Make, model, serial number(if possible)

2) Don't pick it up by placing a pen, etc. in the barrel

3) Make it safe on the spot

4) Photograph potential bullet holes prior to searching

5) Remove section of the wall, etc. to lab for removal of bullets if needed

6) Don't handle with metal forceps/tweezers

How do you search for potential bullet holes?

1) Round shape

2) Bullet wipe

3) GSR(If close enough)

4) Shot pattern(If shotgun)

How do you recover a firearm?

1) Recover in a safe manner.

2) Document the firearm and ammunition

3) Collection of trace evidence.

4) Properly package and seal evidence.

How do you unload a firearm?

1) Always remove ammunition source(mag) first.

2) Open action to ensure chamber is empty

3) Strap action open to ensure it cannot function

How do you unload a revolver?

1) Mark the cylinder to indicate chamber under the hammer

2) Unload each chamber in cylinder noting location

3) Place each cartridge/casing in a separate container

How do you collect a firearm?

Secured in a box, usually with zipties.

How do you collect ammunition?

In paper, plastic, or cardboard containers.

What kinds of Trace DNA can be found on a firearm?

The suspect's skin cells(coarse surfaces) or Latent fingerprints(smooth surfaces).