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Firearms, Tool Marks, and Other Impressions Chapter 8

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Page 1: Fs ch 8 online

Firearms, Tool Marks, and Other Impressions

Chapter 8

Page 2: Fs ch 8 online

Firearms

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Forensic ScienceRichard Saferstein

© 2009 Pearson Education, Upper Saddle River, NJ 07458.

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Handguns Single-shot

Revolvers

Semi-automatic

Automatic

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Forensic ScienceRichard Saferstein

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Revolver

The live rounds are placed into the cylinder

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Forensic ScienceRichard Saferstein

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Revolver

A loaded revolver

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Forensic ScienceRichard Saferstein

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Revolver

Some guns just command your attention

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Revolver

Loading a revolver

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revolvers

Many types

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Forensic ScienceRichard Saferstein

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Revolvers

This one is too pretty to shoot.

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Semi-automatics

Utilize a magazine and internal feeding system

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Semi-automatics

Various models

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Semi-Automatics

Internal workings of a semi-auto

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Semi-automtaics

Stove pipe: The ejected shell casing is jammed in the ejector port

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Forensic ScienceRichard Saferstein

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Long Guns Long guns:-single-shot/repeating/semi-automatic/

automatic

Shotguns-smooth bore

Rifles

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Forensic ScienceRichard Saferstein

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Rifles

Bolt action, pump action and lever action

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Shotguns

Wide varieties

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Shot gun

Another pretty gun

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Introduction Structural variations

Bullet to gun Scratch/abrasion to tool tire track to automobile

Individualization!

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Gun Barrel Markings

steel bar hollowed by drilling

-drill marks: unique

-Bullet picks up marks/unique

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Gun Barrel MarkingsMuskets/pistols: smooth barrels

Rifling: Spin on bullet

LANDS & GROOVES:Lands: Surfaces between grooves

Grooves: Spiral cuts in barrel

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Lands and grooves

Don’t try this at home!

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Gun Barrel Markings Caliber: barrel diameter

Manufacturing rifling process: -class characteristics -consistent

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Striations Striations:

-manufacturing

bullets

-Individual characteristics

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Bullet

Note the striations on the fired bullet. These are unique to the gun that fired it.

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Ammunition

CARTRIDGE/ROUND:

Casing

Bullet

Powder

Primer

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Ammo

Various types of ammunition

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Rifle cartridge

Internal view

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Cartridge

Internal view

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Rifle cartridges

Various calibers

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Firearm Examination

Lands/Grooves/Twist: -start of exam

Match

OR

Eliminate

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The Comparison MicroscopeFor + match:

-Lands/grooves identical widths

-longitudinal striations coincide

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Comparison Microscope

Using a comparison microscope an examiner can view both bullets at once

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Examination

This is an example of two fired bullets. The striations are identical.

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Exams

Another example of matching striations

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Shotguns-smooth barrel

-Shot: pellets

-gauge: Diameter of barrel

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Shot gun shell

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Firing a Weapon1. Trigger pull

2. Hammer falls

3. Firing pin strikes primer

4. Gases ignite/expand

5. bullet out barrel/striations

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Firing a Weapon

Revolver:

-cylinder advances

-shell casings remain in weapon

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Firing a Weapon

Semi-auto:

Ejector: Casing out

Extractor: Next round

Breech lock: Back stop

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Firing a weapon

The hammer falls, hits the firing pin and the powder ignites sending the bullet down and out the barrel. There are a lot of gases and powders that are projected with bullet.

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Cartridge/Shell Case Comparison -ejector

-extractor

-breech lock

-magazine

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Head stamp

The firing pin leaves a unique mark on the primer.

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Yikes

Crime scene investigators nightmare. Each one of these casings needs to be marked, photographed, collected and packaged separately.

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Head stamp

Microscopic comparison of firing pin marks

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Computerized ImagingNational Integrated Ballistics Information

Network, (NIBIN):

bullets Casings firearms

Firearms examiners v. Ballistics!!!!!

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Gunpowder Residue

Muzzle close: Powder on target

Powder patterns: Estimate distance.

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Powder and residue being projected.

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Really being projected.

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Gunpowder ResidueStellate wound: close contact Star shaped Rim of lead

Halo: 12-18 inches

Stippling/Tattooing: 2-3 feet Powder depositBAD PICTURES COMING UP!!!!!!!!!!!!

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Close contact-Stellate wound

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Close contact-Stellate wound

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Impression of gun against skin

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Impression of gun against skin

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Impression of gun against skin

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Stippling

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Example of stippling

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Stippling

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Stippling

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Gunshot wound no stippling

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Gunshot wound entrance

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Gunshot wound exit

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Stellate wound to skull

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GSR on HandsFired weapon:

GSR forward

GSR Back towards shooter

Extremely fragile!

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GSR

Bang! That’s a lot of powder

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GSR Test

This is where you would expect to find GSR and where you swab for it

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GSR

Under a microscope

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Serial Numbers

Criminals obscure:

Permanent on surface

Chemical etching

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Serial restoration kit

Combines acids and electricity to restore serial numbers

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Firearm Evidence CollectionHow do you collect firearms?

Checkered grips

Unload

Record cylinder location

Check for shells/live rounds

Mark/chain of custody

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Firearm Evidence CollectionBullets: Initials

Striation awareness Cotton/pill bottle

Shell casings: Initials

Shotgun shells: Initials

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Tool MarksImpression/cut/gouge/abrasion

Examination:Class characteristics Size/shape

Individual characteristics Minute imperfections

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Tool MarksComparison microscope

Collecting tool marks:

Entire/part of object

Never fit tool into impression!!!!

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Tool marks

Microscopic view

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Other ImpressionsShoe/Tire impressions

Collecting:

Photographs (scale)

Recoverable item to lab

Alternative: Cast/lift

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Impressions

Footwear

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Impressions

Impressions compared to suspect’s shoe

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Impressions

Comparison in progress

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Impressions

Casting footwear impressions in dirt

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Impression

Wax spray is used to preserve footwear impressions in snow

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Impressions

Tire impressions

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Points of ComparisonNumber of points?

New Computer technology

Bite Marks: Food Skin Individual characteristicsPEOPLE SLIDES COMIN UP!!! 4TH ONE IS

ACTUAL DEAD PERSON

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Bite marks

Child abuse case

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Bite marks

Dental stone is used to make a cast impression of bite marks

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Bite mark

Tiger Shark bite mark-no suspect in custody