Ballistic Evidence

BallisticsBallistics

• Ballistics the study of bullets and firearms

• Firearm a weapon, such as a gun, capable of firing a projectile using a confined explosive

Firearms HistoryFirearms History• Matchlock weapons

Relied on wicks to carry a flame to the gunpowder

• Flintlock weaponsRelied on sparks from a piece

of flint to ignite the gunpowder– Could be used in damp

weather

• Percussion weaponsIntroduction of cartridges (a

casing that holds a bullet)

Gun Parts – The BarrelGun Parts – The Barrel

Barrel of a gun is produced from a single rod of steel that has been drilled through the center– Drill markings are different for each type of gun

produced• IE. Shotgun barrels are different than a rifle barrel

– Have different purposes

– Can vary in length

– No two rifled barrels, even those manufactured in succession, will have identical striation markings

Barrel

• Manufacturers also impress the barrel with spiral grooves Known as rifling

• The surfaces of the original bore remaining between the grooves are called lands

Barrel

Each gun manufacturer uses its own technique and own signature amount of lands and grooves– Ex. Smith and Wesson uses five lands and

grooves twisted to the right

Caliber

Caliber of a rifle or handgun is the diameter of the gun barrel– Usually recorded in hundredths of an inch or in

millimeters– Shotguns are measured by gauges

Hammer

Part of the gun that is responsible for beginning the reaction of a bullet firing is the hammer

Breechblock / Ejector

• Breechblock– The rear part of the firearm barrel

Stops the bullet casing from flying through the back of the gun

• EjectorSpits out the empty shell casings to make

room for the next bullet

Bullet / Ammunition

Bullet is a combination of a gunpowder and a projectile– Can be a single bullet or

can be hundreds of buckshot

Back of the bullet contains a firing pin that once struck, ignites the gun powder

Bullet

How A Firearm WorksA Review

• Pull the trigger and the firing pin of the firearm hits the base of the cartridge, igniting the gunpowder mixture

• Gases expand and bullet is propelled forward and case is forced backward

• Bullet is expelled through the barrel – spinning according to the land and groove pattern. The spent casing is ejected from the rear of the gun.

Bullet projection

• As soon as the explosion occurs, the bullet is expelled out through the barrel of the gun

• Bullet is spinning– This is due to the lands and groves in the barrel– This creates markings on the bullet

Opposite Reaction

• Bullet casing is forced backwards against the breechblock

• Casing is the removed via the ejector

Casing Imprints

• Casings are indented with the markings from the weapon’s firing and loading mechanisms:– Hammer– Breechblock– Ejector/extractor

Questions to Answer

1. What type of firearm was used?

2. What was the caliber of the bullet?

3. How many bullets were fired?

4. Where was the shooter standing?

5. What was the angle of impact?

6. Has the firearm been used in a previous crime?

Critical Firearms Evidence

• All of the items below are essential in firearms investigation– The bullet– The weapon– The serial numbers on the weapon– The gunpowder on garments, around wounds,

and on hands

The Weapon

• Safety is of the utmost importance when collecting the weapon

• When collecting a found weapon, it is best to pick it up by the edges of the trigger guard or by the checkered portion of the grip

Weapon Comparison• Once a gun is collected,

a test firing is completed in water to provide a point of comparison for evidence collected with the crime– Remember each weapon

will leave its own unique markings on the ammunition that it is using (both bullet and casing)

Weapon Serial Numbers

• Each weapon has a serial number associated with it– Used for registration and purchasing reasons– Criminalists can track movement of weapons based

on serial number• Most of the time, criminals try to remove the serial number

• Stamped serial numbers put stress on the metal of the gun– When an etching agent is poured on area, the

stressed areas dissolve faster than surrounding metal and reveal the serial number

Collecting A Bullet

• If a bullet is found lodged in something, it is best to remove the surrounding material as to not disturb any of the striations made

• Investigator puts initials on nose or back of bullet

• Wraps it in tissue paper to avoid scratching during transfer

NIBIN

National Integrated Ballistics Network• Combination of NIBIS and Drugfire• United in 2000

• NIBIN networks allows ballistics identification to be conducted on a local, national, or international scale.– This networking feature has been employed to

successfully link crimes between countries.

Measuring DistanceMeasuring Distance

• In cases where a victim has suffered a gunshot wound, it is important to determine the distance from weapon to victim / identify the location of the shooter

Distance is determined primarily by the presence and distribution of certain powder patterns or by the spread of a shot (for a shotgun)

Gunshot Residue (GSR)Gunshot Residue (GSR)

Primers in the bullet contain a blend of different chemicals

Look for the elements Antimony and Barium

Firearm Discharge Firearm Discharge

• When a firearm is discharged, unburned and partially burned particles of gunpowder (in addition to smoke) are propelled out of the barrel, along with the bullet, towards the targetIt is the distribution of gunpowder particles and other

discharge residues around the bullet hole that permits an assessment of the distance from weapon to target

Gunpowder Distribution FactorsGunpowder Distribution Factors

• Factors that influence gunpowder residue on the target:– Barrel length– Caliber– Type of ammunition– Type and condition of weapon fired– Distance from weapon to target

• No GSR will be on target if further than 3 feet

Gunshot Residue DistributionGunshot Residue Distribution

• Handling of a used firearm, the passage of time, and the resumption of normal activities following a shooting, gun shot residue is usually redistributed to other areas– Becomes harder to trace back to original

weapon

Bullet WipeBullet Wipe

Dark ring around the perimeter of the entrance hole in a target– Consists of a mixture

of carbon, dirt, lubricant, primer residue, and lead being wiped off of the bullet

Gunshot Residue DetectionGunshot Residue Detection

• Swab both the firing and nonfiring hand with a 5% solution of nitric acid

or• Use adhesive tape on the hands to pick up

the particles of residue– Tape is put under scanning electron

microscope– More specific than hand swabbing

GSR DetectionGSR Detection

• Infrared photography – used to help find GSR in difficult situations (dark clothing or bloody clothing)

• Greiss test chemical test to develop patterns of GSR around bullet holes– Photopaper is ironed over entrance area– Paper is sprayed with chemical

• Turns GSR pink then blue-violet