1. 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

2. Firearms: A Quick History
Almost every gun is based on the same simple concept: You apply explosive pressure behind a projectile to launch it down a barrel.
The earliest & simplest application of this idea is the cannon.
The 1st handheld guns were essentially mini-cannons; you loaded some gunpowder & a steel ball & lit a fuse

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

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

5. Types of Firearms Handguns (pistols) Revolver Semiautomatic Rifles
Shotguns
Air or BB guns

6. Ammunition
Components
Cartridge case
Primer
Propellant
Projectile

7. Bullets Made of lead, sometimes jacketed with brass, copper, or steel
Bullet size—diameter (caliber or gauge)
Shapes

8. Firearms Identification
Often confused with the term ballistics
Ballistics is the study of a projectile in motion.
Inside the firearm
After it leaves the firearm
When it impacts the target
Identification of Firearms is based upon this basic idea: A harder object marks a softer one & imparts/transfers its microscopic irregularities to that object.

9. Forensic Firearms Expert
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?
Serial Number Restoration
Gunpowder Residue Detection
on clothes, hands, & wounds
Muzzle-to-Target Distances

10. Pulling the Trigger Pulling the trigger releases the firing pin…
The firing pin strikes the primer…
The primer ignites the gun powder…
The powder generates gas that propels the bullet forward through the barrel & ejects the spent cartridge case.

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

16. Bullet Caliber Caliber: the diameter of the gun barrel.
Caliber is recorded in
hundredths of an inch (.22 & .38)
millimeters (9mm)

17. Bullet Anatomy

18. Cartridge Parts & How it works

19. Anatomy of a Bullet

20. Bullet Comparisons
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 grooves to the barrel. This is known as rifling.
Lands: the space between the grooves.
As a spinning bullet passes through the barrel, it is marked by these grooves.

21. Rifling
The grooved spirals inside the barrel of a gun that produce lands and grooves on a bullet
Lands & grooves are class characteristics

22. Striae Scratches on a fired bullet, like a barcode
Can serve as individual evidence
Matching bullets or bullet to a firearm

23. Class Characteristics
Class Characteristics: Once a manufacturer chooses a rifling process, for a particular class of weapon, they keep it consistent.
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.
Class characteristics can eliminate certain makes but are not enough to ID a particular gun.

24. Individual Characteristics
Imperfections in the manufacturing process make each barrel unique.
Rifled barrels, even if made in succession will NOT have identical striation (scratch-like marks).

25. Bullet Comparisons
To match bullets to a gun, test bullets must be fired through a suspect barrel for comparison.
Goddard & Comparison Microscopes
Examined bullets side-by-side (to match striated markings).

26. Cartridge Case Head Stamps Rimfire & Centerfire Cartridges
Usually brass or nickel-clad brass
Class evidence
Manufacturer
Shape
Caliber
Composition
Head Stamps Rimfire & Centerfire Cartridges

27. Cartridge Markings
All moving components contact the cartridge rather than the bullet can leave useful impressions on shell cartridges.
Cartridge Case Individual Characteristics:
Breech face marks
Firing pin impressions
Chamber marks
Extractor marks
Ejector marks

29. Breech Marks
When a cartridge is fired, the explosion forces the bullet down the barrel and the shell casing is forced back against the breech.
This leaves impressions unique to the individual gun’s breech on the shell casing.

30. Breech face Marks

31. Actual Breech Marks

32. Firing Pin Marks
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.
This will in turn leave a distinct impression that is unique to the firing pin of that particular gun.

34. Firing Pin Marks

36. Chamber Marks

37. Ejector Marks

38. Extracting Pin & Ejector Marks
The extracting pin and ejector throw the spent shell casing from the chamber of the gun.
These leave marks on the shell casing that are unique to those parts on that particular firearm.

39. Other Factors Perfect matches sometimes difficult b/c:
Presence of grit & rust in a barrel
Recovered bullets too mutilated or distorted on impact
A spent bullet’s weight can sometimes determine the gun make.
Microgrooves: 8-24 grooves; it’s not as common
General Rifling Characteristics File
FBI database of known land/groove width for all weapons.

40. Shotguns Smooth barrel
Projectile NOT marked as it passes through
Fire small lead balls or pellets contained within a shell.
Characterized by:
diameter of the shot
size & shape of the wad
Gauge: diameter of the barrel
( gauge  diameter)
Identification can still be made by comparison of extractor/ejector markings on shotgun shell.

41. Features of a Semiautomatic Handgun

42. Firearms Evidence Individual: Striae Firing pin marks Breech marks
Extractor marks
Ejector marks
Chamber marks
Class:
Bullet type
Bullet caliber
Bullet weight
Lands and grooves
Rifling
Cartridge case
Head stamp

43. Gunshot Residue (GSR) 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.

44. Gunpowder Chemistry GSR Sources: victim, clothing or target
shooter’s hands
Gunpowder Chemistry
Major detectable elements are: lead (Pb), barium (Ba) & antimony (Sb)
Virtually all cartridge cases are made of brass (copper & zinc); also detectable.

45. Griess Test
Tests for the presence of nitrates (partially burned or unburned gunpowder)
Swab of shooter’s hand
Must produce a pattern for a distance determination

46. Results of GSR Hand Test
Negative results may be caused by:
Washing the hands
Shooter may have been wearing gloves
Lead free ammunition
A rifle or shotgun may not deposit GSR on hands

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

50. 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.

51. DANGER  GRAPHIC IMAGES!

52. Contact Gunshot wound This is a contact gunshot entrance wound.
Since the barrel contacts the skin, the gases released by the fired round go into the subcutaneous tissue & cause the star-shaped laceration.

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

54. Entrance/Exit Wounds
Displayed here is an entrance at the left and an exit at the right.
Exit wounds vary considerably in size and shape because the bullet can be deformed in its transit through the body.
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.
This is a contact range gunshot entrance wound with grey-black discoloration from the burned powder.

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

56. 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.

57. END GRAPHIC IMAGES!

58. Trajectory
DC Sniper

60. SERIAL NUMBER RESTORATION
When a serial number is stamped into a gun, the metal underneath the number is compressed & hardened.
If the number is filed-off, the hardened area may still be present.
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.

61. FIREARMS EVIDENCE COLLECTION
Make sure it is unloaded!!!!!
DO NOT put a pencil into a barrel
REVOLVERS
Indicate location of fired & unfired ammunition
AUTOMATICS
Check magazine for number of rounds
Fingerprint magazine
Place ID tag on trigger guard

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

63. Protect & preserve any residue Air dry if wet
CLOTHING
Protect & preserve any residue
Air dry if wet
Package separately in paper bags
Establish CHAIN OF CUSTODY

64. Toolmarks Tools often used in burglaries may leave a mark.
Class characteristics: type, size, shape
Individual characteristics: features from wear and damage

65. TOOL MARK IMPRESSIONS
Impressions
Cuts
Gouges
Abrasions

66. TOOL MARK IMPRESSIONS COLLECTION
SUBMIT ENTIRE OBJECT
PACKAGE SEPARATELY (ALWAYS!)
DO NOT ATTEMPT TO FIT THE TOOL INTO THE TOOL MARK

67. Matching Toolmarks
Photography & casting are important to match tool with mark ? ?

73. Impressions Shoeprints
Class characteristics— manufacturer, type, model, size
Individual characteristics— wear patterns, nicks, marks, occlusions (like pebbles or sticks)

74. Captured by oblique-angle photography or chemical enhancement
casting in soil
lifting.

75. Treated much the same as shoeprints
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

76. 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.

77. 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

78. Forensics: Debate
Both Sides of the Issue; Gun Control Laws
Should gun sales and ownership be subject to federal regulation?
Introduction
Pro/con sides
Assertion
Evidence
Personal opinion