Forensic BallisticsForensic Ballistics

What is Ballistics?What is Ballistics?

Ballistics is the Ballistics is the science that deals science that deals with the flight, with the flight, behavior and effect of behavior and effect of a projectile.a projectile.

A projectile, such as a A projectile, such as a bullet, is an object bullet, is an object that leaves the source that leaves the source of its energy behind of its energy behind and is effected only and is effected only by gravity.by gravity.

The flight path of the The flight path of the projectile is also projectile is also studied.studied.

Three Categories of BallisticsThree Categories of Ballistics

Internal Ballistics- what physically occurs Internal Ballistics- what physically occurs inside the gun barrel once a projectile is inside the gun barrel once a projectile is fired.fired.

External Ballistics- what physically External Ballistics- what physically happens to the projectile once it leaves the happens to the projectile once it leaves the barrel.barrel.

Terminal Ballistics- how a projectile acts Terminal Ballistics- how a projectile acts when it encounters a target.when it encounters a target.

Forensic BallisticsForensic Ballistics

Forensic Ballistics is Forensic Ballistics is the science of the science of analyzing firearms, analyzing firearms, bullets and bullet bullets and bullet impacts.impacts.

Ballistic fingerprinting Ballistic fingerprinting is analyzing firearm is analyzing firearm evidence to determine evidence to determine if that particular firearm if that particular firearm was used in the crime.was used in the crime.

Categories of FirearmsCategories of Firearms

There are three categories of There are three categories of firearms:firearms:

Handguns – includes pistols, Handguns – includes pistols, revolvers and derringersrevolvers and derringers

Long Guns – includes rifles and Long Guns – includes rifles and shotgunsshotguns

Mounted Guns – includes cannons Mounted Guns – includes cannons and anti-aircraft gunand anti-aircraft gun

Parts of a Handgun Parts of a Handgun An understanding of An understanding of

the parts of any gun is the parts of any gun is essential in forensic essential in forensic ballistics.ballistics.

Parts of a Bolt-Action RifleParts of a Bolt-Action Rifle

Parts of a Pump-Action ShotgunParts of a Pump-Action Shotgun

Components of AmmunitionComponents of Ammunition

In addition to the parts of a gun, it is essential to In addition to the parts of a gun, it is essential to know the components of ammunition.know the components of ammunition.

Bullet Shotgun Shell

Parts of a Gun – The Barrel Parts of a Gun – The Barrel

The diameter of a rifled gun barrel is the caliber.

Caliber is normally recorded in millimeters. For example, a 9 mm handgun.

The Shotgun Barrel

Unlike rifled firearms, shotguns have a smooth barrel.They fire small lead balls or pellets contained within a shotgun shell.The diameter of a shotgun barrel is expressed in terms gauge. The higher the gauge number, the smaller the barrel’s diameter.

Parts of a Gun- The Barrel (cont)Parts of a Gun- The Barrel (cont)

Most gun barrels are Most gun barrels are hollow tubes of hollow tubes of steel. Except for a steel. Except for a shotgun, the inside shotgun, the inside surface of the gun surface of the gun barrel is rifled. barrel is rifled.

The process of rifling The process of rifling creates spiral creates spiral grooves in the grooves in the barrel. The areas barrel. The areas between the grooves between the grooves are called lands.are called lands.

FBI DatabaseFBI Database

The The General Rifling General Rifling Characteristics File Characteristics File is a is a record maintained by the record maintained by the FBI.FBI.

This file lists land and This file lists land and groove width dimensions groove width dimensions for known weapons.for known weapons.

For example, Marlin rifles For example, Marlin rifles undergo a unique rifling undergo a unique rifling process known as process known as microgrooving.microgrooving.

A gun A gun manufactured manufactured by Colt has by Colt has lands and lands and grooves that grooves that have a left have a left hand twist. hand twist.

Are these from Are these from a Colt?.a Colt?.

StriationsStriations

As the bullet travels As the bullet travels through the barrel, the through the barrel, the grooves guide the bullet grooves guide the bullet and cause it to spin.and cause it to spin.

Striations, or fine lines, in Striations, or fine lines, in the gun barrel make the the gun barrel make the same striations on the same striations on the bullet. These striations bullet. These striations are unique to the firearm.are unique to the firearm.

Bullet ComparisonsBullet ComparisonsEvery bullet can be matched to a Every bullet can be matched to a particular weapon through comparing particular weapon through comparing striation marks.striation marks.

Comparison of Reference and Comparison of Reference and Crime Scene BulletsCrime Scene Bullets

When the suspected When the suspected weapon is retrieved, a weapon is retrieved, a reference bullet will be reference bullet will be fired from the gun. fired from the gun. The ballistic fingerprint The ballistic fingerprint of the crime scene of the crime scene bullet is then bullet is then compared to that compared to that reference bullet using reference bullet using a comparison a comparison microscope.microscope.

Is This a Match?

How Exact is the Comparison?How Exact is the Comparison?

A perfect match is rare. A perfect match is rare. Dirt, rust, minute changes in the gun barrel Dirt, rust, minute changes in the gun barrel

as more bullets are fired and distortion of as more bullets are fired and distortion of the bullet on impact may change the the bullet on impact may change the striations.striations.

Other Marks on a Fired BulletOther Marks on a Fired Bullet

Basically, all guns fire Basically, all guns fire by applying explosive by applying explosive pressure behind a pressure behind a projectile to launch it projectile to launch it down a barrel.down a barrel.

This firing process This firing process also leaves unique also leaves unique marks and/or marks and/or impressions on the impressions on the bullet and bullet case.bullet and bullet case.

What is the Firing Process?What is the Firing Process?

The ammunition is loaded into the gun, the hammer is cocked and then the trigger is pulled.

Pulling the trigger initiates the process and a firing pin strikes and ignites the primer.

The primer explodes and ignites the propellant.

What is the Firing Process? (cont)What is the Firing Process? (cont)

As the propellant burns, gases As the propellant burns, gases build up inside the bullet build up inside the bullet case and the bullet is case and the bullet is pushed forward into the pushed forward into the barrel.barrel.

The bullet is forced down the barrel by the expanding gases and the bullet case is slammed back against the breech face.

Imperfections in the barrel and on the breech face are transferred to surfaces of the bullet and bullet case.

What is the Firing Process? (cont)What is the Firing Process? (cont)

As the bullet moves As the bullet moves down the barrel and down the barrel and exits the gun, the exits the gun, the cartridge either stays cartridge either stays in the back of the in the back of the barrel or it is ejected barrel or it is ejected by an ejector by an ejector mechanism.mechanism.

Identifying Marks from the Firing Identifying Marks from the Firing PinPin

Metal-to-metal contact between the bullet Metal-to-metal contact between the bullet case and the firing pin leaves an case and the firing pin leaves an impression on the case. This impression is impression on the case. This impression is in the shape of the firing pin.in the shape of the firing pin.

Identifying Marks from the Breech Identifying Marks from the Breech Face and Ejector MechanismFace and Ejector Mechanism

Markings from the breech Markings from the breech face that occur when the face that occur when the bullet case is slammed bullet case is slammed back as the bullet moves back as the bullet moves forward.forward.

Markings from the ejector Markings from the ejector mechanism that occur mechanism that occur when the bullet case is when the bullet case is ejected from the gun.ejected from the gun.

Identifying marks on a Shotgun Identifying marks on a Shotgun Cartridge ShellCartridge Shell

A shotgun has a A shotgun has a smooth barrel so the smooth barrel so the projectile is not projectile is not marked with any type marked with any type of striation.of striation.

However, the shotgun However, the shotgun cartridge may have cartridge may have the same markings as the same markings as a bullet case.a bullet case.

The Data Base for Firearm The Data Base for Firearm InformationInformation

Originally, the information about firearms, Originally, the information about firearms, ammunition and identifying marks was ammunition and identifying marks was kept by two different agencies; the FBI and kept by two different agencies; the FBI and the ATF&E.the ATF&E.

The FBI maintained a system known as The FBI maintained a system known as DRUGFIRE DRUGFIRE and the ATF&E maintained a and the ATF&E maintained a system known as system known as Integrated Ballistics Integrated Ballistics Identification System (IBIS).Identification System (IBIS).

The Data Base for Firearm The Data Base for Firearm InformationInformation

This two agency system was confusing and unproductive. So in 1999, the two systems were combined into the National Integrated Ballistics Information Network (NIBIN). This system has over 800,000 computerized images.

Gunpowder ResiduesGunpowder Residues

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 target.

Gunpowder ResiduesGunpowder Residues

If the muzzle of the weapon is sufficiently close to the target, gunpowder residue is deposited on the target.

Distance DeterminationDistance Determination

The process of determining the distance between the firearm and the target is usually based on the distribution of powder patterns or the spread of a shot pattern (shotgun).

As the distance increases the residue decreases.

Contact Shot

..

DISTANCE – 9 inches

DISTANCE – 15 inches

DISTANCE – 27 inches

Distance Determination of a Shotgun.Up close, the pellets create similar patterns

as residue.

Distance DeterminationDistance Determination

Distance determination is necessary for Distance determination is necessary for many gunshot wounds. If the shooter many gunshot wounds. If the shooter pleads self-defense, it is very important to pleads self-defense, it is very important to know the distance between the shooter know the distance between the shooter and victim.and victim.

Suicide victims will also have residue on Suicide victims will also have residue on close wounds. Lack of residue may close wounds. Lack of residue may indicate foul play.indicate foul play.

Residue on ClothingResidue on Clothing

Clothing of the victim is chemically tested Clothing of the victim is chemically tested for gunshot residue to confirm the distance for gunshot residue to confirm the distance determination. The Griess Test indicates a determination. The Griess Test indicates a positive result with a color change to pink.positive result with a color change to pink.

Gunshot Residue (GSR) on HandsGunshot Residue (GSR) on Hands

When a weapon is When a weapon is fired residue is fired residue is propelled both propelled both forward and forward and backward.backward.

The residue that is The residue that is propelled backwards propelled backwards leaves traces on the leaves traces on the shooter’s hands as shooter’s hands as well as anyone within well as anyone within very close range.very close range.

GSR on HandsGSR on Hands

The GSR is most The GSR is most likely concentrated on likely concentrated on the thumb web and the thumb web and the back of the firing the back of the firing hand.hand.

The GSR stays on the The GSR stays on the hands for hands for approximately 2 hours approximately 2 hours and is easily removed and is easily removed by washing or wiping by washing or wiping the hands.the hands.

In a suicide, the In a suicide, the hands will be bagged hands will be bagged and tested for GSR at and tested for GSR at the Medical the Medical Examiner’s office.Examiner’s office.

GSR on HandsGSR on Hands

The Dermal Nitrate Test, developed in 1933, was used The Dermal Nitrate Test, developed in 1933, was used for many years. However, it gave many false positives for many years. However, it gave many false positives with cigarette ash, urine and cosmetics.with cigarette ash, urine and cosmetics.

During the test, the suspects hands were covered in During the test, the suspects hands were covered in wax. After the wax hardened it was removed and wax. After the wax hardened it was removed and chemically tested.chemically tested.

A blue color indicated a positive result for GSR.A blue color indicated a positive result for GSR.

Today’s tests for GSR on HandsToday’s tests for GSR on Hands Barium and Antimony are both components in Barium and Antimony are both components in

GSR. Several techniques are used to test for GSR. Several techniques are used to test for these elements.these elements.

1.1. First, the investigator will remove the GSR First, the investigator will remove the GSR particles with tape or swabs.particles with tape or swabs.

2.2. Next, the particles may be examined with a Next, the particles may be examined with a Scanning Electron Microscope, Neutron Scanning Electron Microscope, Neutron Activation Analysis or Flameless Atomic Activation Analysis or Flameless Atomic Absorption Spectrophotometry.Absorption Spectrophotometry.

The presence of Barium and Antimony is The presence of Barium and Antimony is considered a positive for GSR.considered a positive for GSR.

Serial Number RestorationSerial Number Restoration Firearms are “ stamped” Firearms are “ stamped”

with an identification serial with an identification serial number. These numbers number. These numbers are linked to the buyer of are linked to the buyer of the firearm.the firearm.

Identification numbers are Identification numbers are usually etched on the usually etched on the metal body, frame or plate metal body, frame or plate of the gun.of the gun.

Many times, criminals Many times, criminals “erase” the serial number “erase” the serial number and it has to be restored and it has to be restored once the weapon is at the once the weapon is at the crime lab.crime lab.

Serial Number RestorationSerial Number Restoration

To restore a serial number that has been removed or obliterated, the area must be thoroughly cleaned and polished. An etching reagent is applied which will react with the strained area faster than the unaltered metal, allowing the numbers to appear.

Collection and Preservation of Collection and Preservation of Firearm EvidenceFirearm Evidence

FirearmsSafety is the most important precaution,

preventing all accidental discharge of a loaded weapon in transit.

All firearm evidence should be marked for identification with evidence tag attached to the trigger guard.

Firearm recovered from an underwater location should be transported in the submerged in the water found to prevent rust.

AmmunitionBullets recovered at a crime scene are scribed with the investigator’s initials and should be wrapped in tissue paper before transport to protect any trace evidence.

The exact location of shell casings should be noted.

Gunpowder Deposits A firearm victim’s clothing must be preserved to prevent damage or disruption to the gunpowder residues deposited around the bullet hole. Wet clothing should be air dried out of direct sunlight and then folded for protection. Each item should be placed in a separate paper bag.