Firearms• Forensic analysis is vital

to solve a crime that uses a gun.

• In 2004, there were 12,00 homicides in the US

The vast majority of

U.S. homicides involve

guns. And they are more

powerful than ever.

Lansing State Journal, July 2007

Firearms: A Quick History1. Almost every gun is based on the same simple concept: You

apply explosive pressure behind a projectile to launch it down a barrel.

2. The earliest & simplest application of this idea is the cannon. 3. The 1st handheld guns were essentially mini-cannons; you

loaded some gunpowder & a steel ball & lit a fuse

4. War typically resulted in the need for improved weapons technology.

5. In the late 1800’s, the revolver quickly became popular due to it’s size & quick loading.

• It only had to be reloaded every 5-6 shots instead of after each shot.

6. Handguns reigned supreme for the past 200 years & to this day, remain the most popular & readily available firearm.

Types of Firearms

1. Handguns (pistols) – Revolver – Semiautomatic

2. Rifles

3. Shotguns

4. Air or BB guns

Ammunition

Components

1.Cartridge case

2.Primer

3.Propellant

4.Projectile

Bullets

• Made of lead, sometimes jacketed with brass, copper, or steel

• Bullet size—diameter (caliber or gauge)

• Shapes

Firearms Identification

1. Often confused with the term ballistics2. Ballistics is the study of a projectile in motion.

• Inside the firearm• After it leaves the firearm• When it impacts the target

3. Identification of Firearms is based upon this basic idea: A harder object marks a softer one & imparts/transfers its microscopic irregularities to that object.

Forensic Firearms Expert

1. Did a suspect use this gun to kill that person?2. Did these bullets come from that gun?3. Was it really self-defense?4. Is this a case of suicide, or is foul play involved?5. Bullet Comparison6. Weapons Function

– Is it safe? Has it been modified?7. Serial Number Restoration8. Gunpowder Residue Detection

– on clothes, hands, & wounds9. Muzzle-to-Target Distances

Pulling the Trigger

1. Pulling the trigger releases the firing pin…2. The firing pin strikes the primer…3. The primer ignites the gun powder…4. The powder generates gas that propels the

bullet forward through the barrel & ejects the spent cartridge case.

• How a Revolver Works - YouTube.wmv• HOW A GUN WORKS - YouTube.wmv• How A Glock Works - YouTube.wmv

Bullet Caliber1. Caliber: the diameter of the gun barrel.2. Caliber is recorded in

– hundredths of an inch (.22 & .38)– millimeters (9mm)

Bullet Anatomy

Cartridge Parts & How it works

Anatomy of a Bullet

Bullet Comparisons

1. Each gun leaves distinct markings on a bullet passing through it.

2. A gun barrel is made from a solid bar of steel that has been drilled/hallowed out.

3. The drill leaves microscopic marks on the barrel’s inner surface.

4. Gun manufacturers also add spiral grooves to the barrel. This is known as rifling.

5. Lands: the space between the grooves.6. As a spinning bullet passes through the barrel, it is

marked by these grooves.

Rifling

1. The grooved spirals inside the barrel of a gun that produce lands and grooves on a bullet

2. Lands & grooves are class characteristics

Striae

1. Scratches on a fired bullet,2. like a barcode3. Can serve as individual

evidence4. Matching bullets or bullet to

a firearm

Class Characteristics1. Class Characteristics: Once a manufacturer chooses a

rifling process, for a particular class of weapon, they keep it consistent.

2. Lands & Grooves are the same for a model. – .32 caliber Smith & Wesson has 5 lands & grooves twisting to

the right.– .32 caliber Colt has 6 lands & grooves twisting to the left.

3. Class characteristics can eliminate certain makes but are not enough to ID a particular gun.

Individual Characteristics

1. Imperfections in the manufacturing process make each barrel unique.

2. Rifled barrels, even if made in succession will NOT have identical striation (scratch-like marks).

Bullet Comparisons1. To match bullets to a gun, test bullets

must be fired through a suspect barrel for comparison.

2. Goddard & Comparison Microscopes– Examined bullets side-by-side (to match

striated markings).

Cartridge Case

1. Usually brass or nickel-clad brass

2. Class evidence – Manufacturer– Shape– Caliber– Composition

Head Stamps

Rimfire & Centerfire Cartridges

Cartridge MarkingsCartridge Markings1. All moving components contact the

cartridge rather than the bullet can leave useful impressions on shell cartridges.

2. Cartridge Case Individual Characteristics:– Breech face marks– Firing pin impressions – Chamber marks– Extractor marks– Ejector marks

Breech Marks1. When a cartridge is fired, the explosion forces the bullet down the

barrel and the shell casing is forced back against the breech. 2. This leaves impressions unique to the individual gun’s breech on

the shell casing.

Breech face Marks

Actual Breech Marks

Firing Pin Marks1. In order to fire the

cartridge, the primer must first be ignited. To accomplish this a firing pin strikes the center ring of the cartridge.

2. This will in turn leave a distinct impression that is unique to the firing pin of that particular gun.

Firing Pin Marks

Chamber Marks

Ejector Marks

Extracting Pin & Ejector Marks1. The extracting pin

and ejector throw the spent shell casing from the chamber of the gun.

2. These leave marks on the shell casing that are unique to those parts on that particular firearm.

Other Factors

1. Perfect matches sometimes difficult b/c:– Presence of grit & rust in a barrel– Recovered bullets too mutilated or distorted on

impact2. A spent bullet’s weight can sometimes

determine the gun make. 3. Microgrooves: 8-24 grooves; it’s not as

common4. General Rifling Characteristics File

– FBI database of known land/groove width for all weapons.

ShotgunsShotguns1. Smooth barrel

– Projectile NOT marked as it passes through

2. Fire small lead balls or pellets contained within a shell.

3. Characterized by:– diameter of the shot– size & shape of the wad– Gauge: diameter of the barrel

( gauge diameter)

4. Identification can still be made by comparison of extractor/ejector markings on shotgun shell.

Features of a Semiautomatic Handgun

Firearms Evidence

Individual:

1.Striae

2.Firing pin marks

3.Breech marks

4.Extractor marks

5.Ejector marks

6.Chamber marks

Class:1.Bullet type2.Bullet caliber3.Bullet weight4.Lands and grooves5.Rifling6.Cartridge case7.Head stamp

Gunshot Residue (GSR)

1. When a weapon is fired:

- Primer and propellant

particles blow back

toward the shooter.

- Combustion products

(mostly NO2-), unburned

propellant, and particles

of lead follow the bullet,

spreading out with

distance.

1. GSR Sources:– victim, clothing or target– shooter’s hands

2. Gunpowder Chemistry– Major detectable elements are: lead (Pb),

barium (Ba) & antimony (Sb)– Virtually all cartridge cases are made of

brass (copper & zinc); also detectable.

Griess Test

1. Tests for the presence of nitrates (partially burned or unburned gunpowder)

2. Swab of shooter’s hand3. Must produce a pattern for a distance

determination

Results of GSR Hand Test

1. Negative results may be caused by:– Washing the hands– Shooter may have been wearing gloves– Lead free ammunition

2. A rifle or shotgun may not deposit GSR on hands

3. GSR on the hand of a suicide victim, proving he was holding the weapon when it was fired.

4. With a contact or very close range gunshot wound, it is possible to have blood spatter as well as GSR on the hand of the person firing the weapon.

DANGER

GRAPHIC IMAGES!

Contact Gunshot wound

1. This is a contact gunshot entrance wound.

1. Since the barrel contacts the skin, the gases released by the fired round go into the subcutaneous tissue & cause the star-shaped laceration.

Abrasion Ring

1. An abrasion ring, formed when the force of the gases entering below the skin blow the skin surface back against the muzzle of the gun, is seen here in this contact range gunshot wound to the right temple.

2. The abrasion ring, and a very clear muzzle imprint, are seen in this contact range gunshot wound.

Entrance/Exit Wounds

3. This is a contact range gunshot entrance wound with grey-black discoloration from the burned powder.

Displayed here is an entrance at the left and an exit at the right.

1.Exit wounds vary considerably in size and shape because the bullet can be deformed in its transit through the body.

2.There may be no exit wound at all if the bullet's energy is absorbed by the tissues. Some bullets (such a a "hollowpoint") are designed to deform so that all their energy will be converted to tissue damage and not exit.

4. Powder tattooing is seen in this intermediate range gunshot wound. The actual entrance site is somewhat irregular, because the bullet can tumble in flight.

5. The surface of the skull demonstrates the heavy soot in this contact range entrance wound, as well as radiating fracture lines. The direction of fire was thus toward the back of this picture.

END GRAPHIC IMAGES!

Trajectory

SERIAL NUMBER RESTORATION1. When a serial number is stamped into a gun,

the metal underneath the number is compressed & hardened.

2. If the number is filed-off, the hardened area may still be present.

3. By using an acid solution the metal can be slowly eaten away.

– In this process the softer metal will be eaten away first and the number may reappear.

1. Make sure it is unloaded!!!!! 2. DO NOT put a pencil into a barrel3. REVOLVERS

– Indicate location of fired & unfired ammunition4. AUTOMATICS

– Check magazine for number of rounds– Fingerprint magazine

5. Place ID tag on trigger guard

FIREARMS EVIDENCE COLLECTION

6. AMMUNITION– Write on base or nose– Package in pill box or envelope– Wrap in tissue to protect

7. CLOTHING– Protect & preserve any

residue– Air dry if wet– Package separately in

paper bags8. Establish CHAIN OF

CUSTODY

Toolmarks

1. Tools often used in burglaries may leave a mark.

2. Class characteristics: type, size, shape

3. Individual characteristics: features from wear and damage

TOOL MARK IMPRESSIONS1. Impressions

2. Cuts

3. Gouges

4. Abrasions

TOOL MARK IMPRESSIONS COLLECTION

1. SUBMIT ENTIRE OBJECT

2. PACKAGE SEPARATELY (ALWAYS!)

3.3. DO NOTDO NOT ATTEMPT TO FIT THE TOOL INTO THE TOOL MARK

Matching Toolmarks

• Photography & casting are important to match tool with mark

?

?

Impressions

1. Shoeprints– Class characteristics—

manufacturer, type, model, size

– Individual characteristics— wear patterns, nicks, marks, occlusions (like pebbles or sticks)

– Captured by oblique-angle photography or chemical enhancement

– casting in soil– lifting.

2. Tire marks– Treated much the same as shoeprints– Class characteristics involve design, size, type, and model.– Wear and damage cause defects that can lead to

individualization.– TreadMate is a database containing data on more than

5,000 vehicle tires and tread patterns.

Tire Treads

3. Bite marks– Result from assault or

sexual attack, common in domestic violence

– Individual evidence, if enough impressions

– Bite marks were the prime evidence in the conviction of serial killer Ted Bundy.

4. Serial Numbers/Restoration of serial numbers

– Items of value may have ID numbers stamped into them.

– Grinding is usually used to obliterate identification numbers.

– To restore ID numbers on metal, an acid etching solution is employed.

HCl-CuCl2

Forensics: Debate

Should gun sales and ownership be subject to federal regulation?

• Introduction

• Pro/con sides

• Assertion

• Evidence

• Personal opinion

Both Sides of the Issue; Gun Control Laws