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TODAY: 1.  DID YOU TURN IN YOUR

“HANDWRITING ANALYSIS CASE STUDY”? DUE BY THURSDAY!!

2.   Start Ballistics Notes 3.   Complete CSI

•  OBJECTIVE: •  To explain how bullets are

test fired and matched. •  DO NOW:

•  What are the parts of cartridge?

MAY 15, 2012 – “F” DAY TODAY: 1.  Six Samples Lab 2.   Exercise 17-2

DUE DATES: •  Handwriting Case Studies

due TOMORROW! •  Exercise 17-2 Due

Monday

•  OBJECTIVE: •  To explain how bullets

are test fired and matched.

•  DO NOW: •  What causes a bullet to

“fire”?

MAY 16, 2012 – “A” DAY

FORENSICS OF FIREARMS & BALLISTICS

TRUE OR FALSE…

•  Most homicides (murders) are caused by firearms.

ANSWER

•  TRUE… sort of.

•  United States: 60% of homicides involve firearms •  Finland: 20%, Mexico 26%, Columbia 83%

•  Point: Definitely worth studying in forensics!

•  Gunpowder was invented in China over 1000 years ago. Made of potassium nitrate (KNO3), sulfur (S), and charcoal (carbon).

•  Matchlock firearms used matches to light a fuse called “slow match”. The slow match then would ignite gunpowder and fire a lead ball (invented in the mid 1400’s)

HISTORY OF FIREARMS

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•  Flintlock firearms came into use in the early 1700’s. They use a spark caused by flint striking steel to ignite the gunpowder, making them more reliable in damp weather.

•  Both matchlocks and flintlocks were mostly “muskets” – loaded by the muzzle (front end) and with a smooth bore (not rifled). They were the primary firearms used in the Revolutionary War.

HISTORY OF FIREARMS

•  Caplock or percussion cap firearms were an improvement (dating from 1839) that was a step closer to the modern bullet. A “cartridge” held the bullet (lead ball) and the gunpowder so that they didn’t have to be loaded separately. Then a separate “percussion cap” held the primer that ignited the gunpowder. This sped up the loading process considerably.

HISTORY OF FIREARMS

•  Rifles – have a “rifled” barrel (grooves running down the inside of the barrel in a spiral pattern). They came into use in the 1500’s but didn’t become dominant until the mid 1800’s (think Civil War). Note that a matchlock or a flintlock could have been either a musket (no rifling) or a rifle (smooth rifling).

HISTORY OF FIREARMS WHAT IS THE PURPOSE OF RIFLING? •  A) makes firearm more accurate •  B) makes the firearm more powerful and do more damage •  C) makes the firearm easier to use •  D) costs less money to produce

WHY DID FIREARMS REPLACE BOWS AND CROSSBOWS IN WARFARE?

•  A) Muskets were more powerful & could penetrate armor better •  B) Muskets had a greater range •  C) Muskets cost less to produce •  D) Muskets were easier to use

•  Cartridges are what people now think of as “bullets” – the combination of a projectile (bullet), the gunpowder, and the primer all in one case. This made loading much easier and faster.

HISTORY OF FIREARMS

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•  Grooves and ridges (lands) in the barrel of a gun produce the twisting that adds accuracy (comparison to football…)

•  These grooves leave individualized markings on the bullet

RIFLING COMPARISON OF RIFLE MARKINGS ON BULLET

(DONE USING COMPARISON MICROSCOPE)

More on this and other markings later…

BULLET CALIBER

•  Caliber refers to the diameter of the bullet (usually!) •  If you have heard of a “22” or a “9mm” or a “45” these all refer to

caliber - usually measured in inches (a 22 is 0.22 inches in diameter) - some measured in millimeters (9mm)

Forensic Value: Caliber provides a class characteristic that is very useful in the process of matching a gun to a given crime or suspect. A 9mm bullet simply cannot be fired from a .45 caliber gun (or any other caliber). A CSI can determine caliber easily with cartridge casings, or with more difficulty by measuring a fired bullet found at a crime scene.

VARIOUS CALIBERS OF BULLETS

1: 12 Gauge shotgun shel 2: AA battery 3: .454 Casull 4: .45 Winchester Magnum 5: 0.44 Remington Magnum 6: .357 Magnum 7: .38 Special 8: .45 ACP 9: .38 Super 10: 9mm Luger 11: .32 ACP 12: .22 LR

Note that the length of the bullet is important, but not part of how it is commonly named.

•  Have a shell case or cartridge? Easy. It’s on the bottom of the case (or can be identified from the manufacturer’s writing.)

•  Have the gun? Easy. It’s

usually marked on the firearm or can be looked up based on the make/model of the firearm.

IDENTIFYING BULLET CALIBER

If you only have a bullet from a crime scene… harder. -  Measure bullet diameter with

calipers and compare to common calibers

-  Weigh it and compare to common bullet weights (measured in grains)

-  Problem: bullets often become highly deformed by passing through bodies and/or hitting hard objects such as walls

IDENTIFYING BULLET CALIBER

1 grain = 64.8 mg

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Handgun vs. Long Gun

A handgun is designed to be usable with one hand, so it has a short barrel. A long gun has a longer barrel and generally requires 2 hands to use.

BASIC TERMINOLOGY •  A revolver has a revolving

cylinder containing the cartridges. The shell cases are NOT ejected when fired.

•  A pistol lacks a cylinder; virtually all modern handguns are “semi-automatics” with the cartridges in a magazine (sometimes called a “clip”)

TERMINOLOGY -- HANDGUNS revolver

cylinder

Semi-automatic pistol

•  Long guns primarily include rifles and shotguns.

•  The difference is in the cartridge. Rifle cartridges typically contain one bullet, while a shotgun “shell” contains many small pellets called “shot”. Also, a shotgun barrel is not rifled. The size of the barrel is measured in “gauge” (ex: 12 gauge or 20 gauge).

TERMINOLOGY – LONG GUNS Shotgun shells – various gauges

Lead shot for shotguns

TERMINOLOGY – PARTS OF A REVOLVER

HOW A FIREARM WORKS (THE BASICS)

1) Cocking the firearm pulls the firing pin back under tension with a spring

2) Pulling the trigger releases the firing pin.

3) The firing pin hits the base of the cartridge, igniting the primer powder

4) The primer powder sparks through the flash hole to gunpowder

5) Pressure from rapid combustion pushes bullet out of shell case

6) The bullet follows the lands and grooves and spirals out of the barrel

MATCHING BULLETS AND SHELL CASES TO FIREARMS

•  Test-firing: the suspect’s firearm must be test-fired into water or ballistic gel •  Creates known sample •  Water/gel prevents bullet from being deformed

•  Firing pin marks •  Caused by firing pin striking shell case •  can be used to get individual match a cartridge to a firearm

•  Breechblock marks •  Marks left on the shell case; produced when the cartridge casing slams

backward and strikes the breechblock •  Extractor & Ejector marks – the mechanism that kicks out the used shell

case after the gun is fired leaves scratches/marks on the shell case

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TEST-FIRING TANK FIRING PIN IMPRESSIONS

DO THESE TWO MATCH? DO THESE TWO MATCH?

DO THESE TWO MATCH? DO THESE TWO MATCH?

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EXTRACTOR MARKS MATCHING BULLETS TO FIREARMS

(RIFLING MARKS) •  Caliber provides only a class match •  Every rifled barrel is slightly different – •  left or right twist of rifling •  number of lands and grooves (many have 6; some have 8, 10, etc.) •  imperfections in the lands and groves scratch bullet in unique way A bullet is test-fired, then analyzed under a comparison microscope that allows you to look at a side-by-side image of the test-fired bullet and the crime scene bullet

TWO TYPES OF RIFLING

Lands and Groves (the one below has 8 lands and 8 groves)

Polygonal Rifling Flattened sides – this one makes an octagon

RIFLING MARKS ON BULLETS – DO THEY MATCH?

RIFLING MATCH USING COMPARISON MICROSCOPE

GUNSHOT RESIDUES (GSR)

•  Determine whether or not someone recently fired a gun •  Particles of unburned powder, tiny amounts of lead from

the bullet, and traces of smoke (nitrates) •  Leave traces on the hand, arm, face, hair, or clothing of

the shooter and/or victim •  Chemical testing can detect lead and nitrate residue

(sometimes even if washing is attempted)

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GUNSHOT IN SHIRT…

Black mark = “bullet wipe” Black specks around bullet wipe = unburned gunpowder

FIRING DISTANCE DETERMINATION

•  Distance from victim to shooter can be determined by examining the residue pattern on the victim or victim’s clothing (specks of unburned gunpowder)

•  A more spread-out pattern means the gun was father away •  At point-blank (contact) range, burn marks are left on skin/

clothing •  Only works out to about 3 feet •  Test-firing is necessary to create a reference (guns &

powder amounts vary)

TRAJECTORY BULLETS THROUGH GLASS

•  Some crime scenes involve a bullet going through the window of a car, house, store, etc

•  Determining direction of fire can be very important •  Exit hole larger than entrance hole •  Sequence of shots determined by how radial cracks run

into one another (diagram on board) Picture of Bullet Holes in Glass

QUESTIONS TO GET YOU THINKING…

1.  Why do entrance wounds tend to be smaller than exit wounds?

2.  Why does direction of bullet penetration matter to investigators?

3.  If the bullet penetrates clothing, what can fibers embedded in the wound indicate?

4.  If the gun is fired with the muzzle touching the victims clothing skin, what telltale mark may show up?