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
4. War typically resulted in the need for improved weapons technology.
5. 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.
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.
2.
3.
4.
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
3. Identification of Firearms is based upon this basic idea: A _______________________________
marks a _________________________ & imparts/transfers its _________________________________
____________________________________________ to that object.
Forensic Firearms Expert
1.
2.
3.
4.
5.
6.
Did a suspect use this gun to kill that person?
Did these bullets come from that gun?
Was it really self-defense?
Is this a case of suicide, or is foul play involved?
Bullet Comparison
Weapons Function
– Is it safe? Has it been modified?
7. Serial Number Restoration
8. Gunpowder Residue Detection
– on clothes, hands, & wounds
9. Muzzle-to-Target Distances
Pulling the Trigger
1.
2.
3.
4.
Pulling the trigger releases the ________________________________
The firing pin strikes the ______________________________
The primer ignites the ______________________________
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)
Cartridge
How it Works
Bullet Anatomy
Cartridge
Parts Parts
& Howand
it works
Cartridge Case
Lead Bullet
Primer
Gun Powder
Bullet Comparisons
1.
2.
3.
4.
5.
6.
Each gun leaves distinct markings on a bullet passing through it.
A gun barrel is made from a solid bar of steel that has been drilled/hallowed out.
The drill leaves microscopic marks on the barrel’s inner surface.
Gun manufacturers also add spiral ___________ to the barrel. This is known as ___________
Lands: _______________________________________________________
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.
2.
3.
4.
____________________ on a fired bullet,
like a ____________________
Can serve as __________________________________
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 __________
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 ________________
2. Rifled barrels, even if made in succession _______________have identical striation
(scratch-like marks).
Bullet Comparisons
1. To match bullets to a gun, ___________________________________________________________________
_________________________________________________________________________________________________
2. Goddard & Comparison Microscopes
– 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.
Extracting Pin and Ejector Marks
The extracting
and ejector th
the spent shel
casing from th
chamber of th
gun.
These leave m
on the shell ca
that are uniqu
those parts on
particular firea
Other Factors
1. Perfect matches sometimes difficult b/c:
– Presence __________________________________________________________________
– Recovered bullets too mutilated or distorted on impact
2. A spent bullet’s _________________________ can sometimes determine the gun make.
3. Microgrooves: 8-24 grooves; it’s not as common
4. General Rifling Characteristics File
– FBI database of known land/groove width for all weapons.
Shotguns
1. _____________________________________________
– Projectile NOT marked as it passes through
2. Fire small _____________________ or __________________ contained within a shell.
3. Characterized by:
– ______________________ of the shot
– ______________________ of the wad
– Gauge: _____________________________________________________________________________
2. Identification can still be made by comparison of ____________________________________
markings on shotgun shell.
Firearms Evidence
Individual:
1. ________________________________________
2. ________________________________________
3. ________________________________________
4. ________________________________________
5. ________________________________________
6. ________________________________________
Gunshot Residue (GSR)
Class:
1. _______________________________________
2. _______________________________________
3. _______________________________________
4. _______________________________________
5. _______________________________________
6. _______________________________________
7. Head stamp
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.
2. GSR Sources:
- _______________________________________________________________________________________
- _______________________________________________________________________________________
3. 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 ____________________
– ___________________________________________________
2. 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.
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.
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
______________________________________________________________
5. 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
– __________________________________________________________________________________________
4. AUTOMATICS
– __________________________________________________________________________________________
– __________________________________________________________________________________________
5. Place ID tag on trigger guard
6. AMMUNITION
– Write on base or nose
– Package in ____________________ or _______________________
– Wrap in ______________________________________________________
7. CLOTHING
– __________________________________________________________________________________________
– __________________________________________________________________________________________
– Package separately in ________________________________________________________________
8. 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.
2.
3.
4.
Impressions
Cuts
Gouges
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.
2. 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.
3. 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.
4. 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.