Chapter 15 – Firearms, Toolmarks, & Impressions

Firearms

  1. ______is vital to solve a crime that uses a gun.
  2. In 2004, there were ______homicides in the US

Firearms: A Quick History

  1. Almost every gun is based on the same simple concept: You apply explosive ______behind a ______to launch it down ______
  2. The earliest & simplest application of this idea is the ______
  3. The 1st handheld guns were essentially mini-cannons; you loaded some gunpowder & a steel ball & lit a fuse
  1. War typically resulted in the need for improved weapons technology.
  2. In the late 1800’s, the revolver quickly became popular due to its size & quick loading.

•It only had to be reloaded every ______shots instead of after each shot.

  1. 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

  1. Rifles
  2. Shotguns
  3. Air or BB guns

Ammunition Components

Bullets

•Made of ______, sometimes jacketed with ______

•Bullet size—diameter (caliber or gauge)

•Shapes

Firearms Identification

  1. Often confused with the term ballistics
  2. Ballistics is the study of ______

•Inside the firearm

•After it leaves the firearm

•When it impacts the target

  1. Identification of Firearms is based upon this basic idea: A ______marks a ______& imparts/transfers its ______
    ______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 Comparison
  6. Weapons Function

–Is it safe? Has it been modified?

  1. Serial Number Restoration
  2. Gunpowder Residue Detection

–on clothes, hands, & wounds

  1. Muzzle-to-Target Distances

Pulling the Trigger

  1. Pulling the trigger releases the ______
  2. The firing pin strikes the ______
  3. The primer ignites the ______
  4. The powder generates gas that ______forward through the ______ejects the spent ______.

Bullet Caliber

  1. Caliber: ______
  2. Caliber is recorded in

–hundredths of an inch (.22 & .38)

–millimeters (9mm)

Bullet Anatomy

Cartridge Parts & How it works

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 ______to the barrel. This is known as ______
  5. Lands: ______
  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 ______and ______on a bullet
  2. Lands & grooves are ______

Striae

  1. ______on a fired bullet,
  2. like a ______
  3. Can serve as ______
  4. Matching bullets or bullet to a firearm

Class Characteristics

  1. 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 ______lands & grooves twisting to the ______

–.32 caliber Colt has ______lands & grooves twisting to the ______

  1. 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 ______
  2. Rifled barrels, even if made in succession ______have identical striation (scratch-like marks).

Bullet Comparisons

  1. To match bullets to a gun, ______
    ______
  2. GoddardComparisonMicroscopes

–Examined bullets side-by-side (______).

Cartridge Case

  1. Usually ______
  2. Class evidence

–Manufacturer

–Shape

–Caliber

–Composition

Cartridge Markings

  1. All moving components contact the cartridge rather than the bullet can leave useful impressions on ______.
  2. Cartridge Case Individual Characteristics:

–Breech face marks

–Firing pin impressions

–Chamber marks

–Extractor marks

–Ejector marks

Breech Marks

  1. When a cartridge is fired, the ______forces the ______down the barrel and the shell casing is ______against the breech.
  2. This leaves impressions unique to the individual gun’s ______on the shell casing.

Firing Pin Marks

  1. In order to fire the cartridge, the ______must first be ignited. To accomplish this a ______strikes the ______of the cartridge.
  2. This will in turn leave a distinct impression that is unique to the firing pin of that particular gun.

Chamber Marks

Extracting Pin & Ejector Marks

  1. The ______and ______throw the spent shell casing from the chamber of the gun.
  2. These leave marks on the ______that are unique to those parts on that particular firearm.

Other Factors

  1. Perfect matches sometimes difficult b/c:

–Presence ______

–Recovered bullets too mutilated or distorted on impact

  1. A spent bullet’s ______can sometimes determine the gun make.
  2. Microgrooves: 8-24 grooves; it’s not as common
  3. General Rifling Characteristics File

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

Shotguns

  1. ______

–Projectile NOT marked as it passes through

  1. Fire small ______or ______contained within a shell.
  2. Characterized by:

–______of the shot

–______of the wad

–Gauge: ______

  1. Identification can still be made by comparison of ______markings on shotgun shell.

Firearms Evidence

Individual:

  1. ______
  2. ______
  3. ______
  4. ______
  5. ______
  6. ______

Class:

  1. ______
  2. ______
  3. ______
  4. ______
  5. ______
  6. ______
  7. Head stamp

Gunshot Residue (GSR)

  1. When a weapon is fired:

-______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:

-______

-______

  1. Gunpowder Chemistry

-Major detectable elements are: ______

-Virtually all cartridge cases are made of brass (copper & zinc); also detectable.

Griess Test

  1. Tests for the presence of ______(partially burned or unburned gunpowder)
  2. ______
  3. Must produce a pattern for a distance determination

Results of GSR Hand Test

  1. Negative results may be caused by:

–______

–Shooter may have been ______

–______

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

–GSR on the hand of a suicide victim, proving he was ______when it was fired.

  1. 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.

Contact Gunshot wound

  1. This is a contact gunshot entrance wound.
  2. Since the barrel contacts the skin, the gases released by the fired round go into the ______& cause the ______

Abrasion Ring

  1. An ______, formed when the force of the ______entering below the skin blow the skin surface back against the ______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

  1. ______vary considerably in size and shape because the bullet can be ______in its transit through the body.
  2. There may be no exit wound at all if the bullet's energy is ______by the tissues. Some bullets (such a a ______) are designed to ______so that all their energy will be converted to ______and not ______
  3. This is a contact range gunshot entrance wound with grey-black discoloration from the burned powder.
  4. ______is seen in this intermediate range gunshot wound. The actual entrance site is somewhat ______, because the bullet ______
  1. The surface of the skull demonstrates the ______in this contact range ______, as well as ______. The direction of fire was thus toward the back of this picture.

SERIAL NUMBER RESTORATION

  1. When a ______is stamped into a gun, the metal underneath the number is ______
  2. If the number is filed-off, the ______
  3. By using an acid solution the metal can be slowly eaten away.

–In this process the ______will be eaten away first and the number may reappear.

FIREARMS EVIDENCE COLLECTION

  1. Make sure it is ______
  2. DO NOT put a pencil into a barrel
  3. REVOLVERS

–______

  1. AUTOMATICS

–______

–______

  1. Place ID tag on trigger guard
  2. AMMUNITION

–Write on base or nose

–Package in ______or ______

–Wrap in ______

  1. CLOTHING

–______

–______

–Package separately in ______

  1. Establish CHAIN OF CUSTODY

Toolmarks

  1. Tools often used in burglaries may leave a mark.
  2. Class characteristics: ______
  3. Individual characteristics: ______

TOOL MARK IMPRESSIONS

  1. Impressions
  2. Cuts
  3. Gouges
  4. Abrasions

TOOL MARK IMPRESSIONS COLLECTION

  1. ______
  2. ______
  3. DO 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— ______

–Individual characteristics— ______
______

–Captured by oblique-angle photography or chemical enhancement

–______

–lifting.

  1. Tire marks

–Treated much the same as shoeprints

–Class characteristics involve______

–______cause defects that can lead to individualization.

–______is a database containing data on more than 5,000 vehicle tires and tread patterns.

  1. Bite marks

–Result from ______or ______, common in domestic violence

–Individual evidence, if enough impressions

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

  1. Serial Numbers/Restoration of serial numbers

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

–______is usually used to obliterate identification numbers.

–To restore ID numbers on metal, ______is employed.