Fs Ch 8

Firearms, Tool Marks, and Other Impressions

Chapter 8

Firearms

Quite the collection of fireamrs

Forensic ScienceRichard Saferstein

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

All Rights Reserved.3

Handguns Single-shot

Revolvers

Semi-automatic

Automatic




Revolver

The live rounds are placed into the cylinder




Revolver

A loaded revolver




Revolver

Some guns just command your attention




Revolver

Loading a revolver




revolvers

Many types




Revolvers

This one is too pretty to shoot.




Semi-automatics

Utilize a magazine and internal feeding system




Semi-automatics

Various models




Semi-Automatics

Internal workings of a semi-auto




Semi-automtaics

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




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

automatic

ShotgunsShotChoke

RiflesLands and grooves




Rifles

Bolt action, pump action and lever action




Shotguns

Wide varieties




Shot gun

Another pretty gun




Introduction Structural variations/irregularities

A bullet to a gun A scratch or abrasion mark to a single

tool A tire track to a particular automobile

Individualization: firearm/tool mark examination.




Gun Barrel Markings

Gun barrel: steel bar hollowed by drilling.

Drill marks: randomly irregular/unique

Bullet picks up marks of barrel/unique to each gun.

Particular to each gun.




Gun Barrel MarkingsMuskets/pistols: smooth barrels/poor accuracy &

range

Rifling: Spin on bullet

Lands: Surfaces between grooves

Grooves: Spiral cuts in barrel







Lands and grooves

Don’t try this at home!







Gun Barrel Markings Caliber: barrel diameter

Manufacturing rifling process: class characteristics remain consistent.




Striations Striations:

Manufacturing Process

Left on bullets

Individual characteristics of barrel.

Striations: No 2 alike.




Bullet

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




Ammunition

CARTRIDGE/ROUND:

Casing

Bullet

Powder

Primer




Ammo

Various types of ammunition




Rifle cartridge

Internal view




Cartridge

Internal view




Rifle cartridges

Various calibers




Firearm Examination

Lands/Grooves/Twist: Start of exam

Differences: Eliminate as suspect.




The Comparison Microscope Comparison microscope: #1 tool

Not only must the lands and grooves of the test and evidence bullet have identical widths, but the longitudinal striations on each must coincide.




Comparison Microscope

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




Examination

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




Exams

Another example of matching striations




Shotguns Smooth barrel.

Shot: Small pellets.

Gauge: Diameter of barrel.

High gauge=small diameter




Shot gun shell




Firing a WeaponTrigger pull:

Hammer falls

Firing pin strikes primer

Gases ignite and expand

Forcing bullet of barrel/picks up striations




Firing a Weapon

Revolver:

Cylinder advances

Shell casings remain in weapon

5-8 rounds




Firing a Weapon

Semi-auto:

Ejector: Casing out

Extractor: Next round

Breech lock: Back stop

All metal parts




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.




Cartridge/Shell Case ComparisonFiring pin: Primer

Shell casing: Ejector Extractor Breech lock Magazine




Yikes

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




Head stamp

The firing pin leaves a unique mark on the primer.




Head stamp

Microscopic comparison of firing pin marks




Computerized ImagingNational Integrated Ballistics Information

Network, (NIBIN): Bullets Shell casings Retrieved firearms

Firearms examiners v. Ballistics!!!!!




Gunpowder ResidueFirearm discharged: Powder particles

propelled.

Muzzle close: Powder on target.

Powder patterns: Estimate distance.




Powder and residue being projected.




Really being projected.




Gunpowder ResidueStellate wound: Close contact (<1 inch) Star shaped Rim of lead

Halo: 12-18 inches

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




Close contact-Stellate wound




Close contact-Stellate wound




Impression of gun against skin












Stippling







Example of stippling




Stippling




Stippling







Gunshot wound no stippling




Gunshot wound entrance




Gunshot wound exit




Stellate wound-close contact













Stellate wound to skull




GSR on HandsFired weapon:

GSR forward

GSR Back towards shooter

Extremely fragile

Valuable information




GSR

Bang! That’s a lot of powder




GSR Test

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




GSR

Under a microscope




Serial Numbers

Criminals obscure:

Permanently stamped under surface

Chemical etching




Serial restoration kit

Combines acids and electricity to restore serial numbers




Firearm Evidence CollectionHow do you collect firearms?

Checkered grips Prevent AD Unload Record cylinder location Check for shells/live rounds Mark/chain of custody




Firearm Evidence CollectionBullets: Initials

Striation awareness Cotton/pill bottle

Shell casings: Initials

Shotgun shells: Initials




Tool MarksImpression, cut, gouge, or abrasion

Examination:Class characteristics Size/shape

Individual characteristics Minute imperfections Wear/age




Tool MarksComparison microscope: #1 instrument used.

Collecting tool marks:

Entire/part of object

Never fit tool into impression!!!!




Tool marks

Microscopic view







Other ImpressionsShoe/Tire: Important evidence.

Collecting:

Photographs (scale)

Recoverable item to lab

Alternative: Cast/lift




Impressions

Footwear




Impressions

Impressions compared to suspect’s shoe




Impressions

Comparison in progress




Impressions

Casting footwear impressions in dirt




Impression

Wax spray is used to preserve footwear impressions in snow




Impressions

Tire impressions




Points of ComparisonNumber of points?

New Computer technology

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

ACTUAL DEAD PERSON




Bite marks

Child abuse case




Bite marks

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




Bite mark

Tiger Shark bite mark-no suspect in custody




You decide

Victim of attack. What did it?




You decide

Examine the open wounds to the neck. Still don’t know? You will never guess!







Solution

Here is the suspect. The victim was a tiger trainer who was in the enclosure when the tiger put his paws on the victim’s shoulders, opened his mouth and took the victim’s entire head into mouth. The tiger then just bit down and severed both the carotid arteries and the jugular veins.

The tiger was less than impressed to have his picture taken.

Fs Ch 8

Sports

gun barrel markings

gun shell

striations striations

bullet lands

diameter of barrel

pretty gun

gun barrel markings

casing bullet powder