firearms toolmarks and impressions. types of firearms handguns (pistols) revolver semiautomatic...

FIREARMS TOOLMARKS AND IMPRESSIONS

TYPES OF FIREARMSHANDGUNS (PISTOLS) REVOLVER

SEMIAUTOMATIC

RIFLES

SHOTGUNS

AIR OR BB GUNS

AMMUNITION

CARTRIDGE CASE PROPELLANT

PRIMER PROJECTILE

Components:

BULLETS MADE OF LEAD, SOMETIMES JACKETED WITH BRASS, COPPER, OR STEEL

Bullet size—diameter (caliber or gauge)

Shapes

RIFLING THE GROOVED SPIRALS INSIDE THE BARREL OF A GUN THAT PRODUCE LANDS AND GROOVES ON A BULLET

Lands and grooves are class characteristics.

STRIAE

SCRATCHES ON A FIRED BULLET, LIKE A BARCODE,

that can serve as individual evidence, matching bullets or bullet to a firearm

CARTRIDGE CASE USUALLY BRASS OR NICKEL-CLAD BRASS

Head stamps

Rimfire and

centerfire cartridges

Class evidence

CARTRIDGE CASE, CONTINUEDINDIVIDUAL CHARACTERISTICS

Firing pin marks

Breech marksExtractor marks

FEATURES OF A SEMIAUTOMATIC HANDGUN

FIREARMS EVIDENCEINDIVIDUAL:

STRIAE

FIRING PIN MARKS

BREECH MARKS

EXTRACTOR MARKS

EJECTOR MARKS

CHAMBER MARKS

Class:Bullet typeBullet caliberBullet weightLands and groovesRiflingCartridge caseHead stamp

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.

DISTANCE TO TARGET

THE GREISS TEST CONVERTS NITRITES TO AN ORANGE-RED COLOR.

SODIUM RHODIZONATE REACTS WITH TRACES OF LEAD TO MAKE PURPLE SPOTS.

Comparison Microscope• The single most important tool for a

firearms examiner • Two bullets can be observed and compared

simultaneously within the same field of view

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

IDENTIFICATION

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Computerized Imaging • Computerized imaging technology has made it

possible to store bullet and cartridge surface characteristics similarly to automated fingerprint files

• The National Integrated Ballistics Information Network (NIBIN) produces database files from bullets and cartridge casings retrieved from crime scenes or test fires from retrieved firearms, often linking a specific weapon to multiple crimes

• It is important to remember, however, that the ultimate decision for making a final comparison must be determined by the forensic examiner through traditional microscopic methods

IDENTIFICATION (CONTINUED)

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TOOLMARKSTOOLS OFTEN USED IN BURGLARIES MAY LEAVE A MARK.

Class characteristics: type, size, shape

Individual characteristics: features from wear and damage

LAB ACTIVITY: MATCHING TOOLMARKS

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Photography and casting are important to match tool with mark.

Tool MarksA tool mark is any impression, cut, gouge, or abrasion caused by a tool coming into contact with another object

A careful examination of the impression can reveal important class characteristics, such as the size and shape of the tool

It is the presence of minute imperfections on a tool that imparts individuality to it

The shape and pattern of such imperfections are further modified by damage and wear during the life of the tool

• The comparison microscope is used to compare crime scene tool marks with test impressions made with the suspect tool

• When practical, the entire object or the part of the object bearing the tool mark should be submitted to the crime laboratory for examination

• Under no circumstances should the crime scene investigator attempt to fit the suspect tool into the tool mark

• Any contact between the tool and the marked surface may alter the mark and will, at the least, raise serious questions about the integrity of the evidence

TOOL MARKS AND OTHER IMPRESSIONS

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• Abrasion mark – a mark produced when a surface slides across another surface

• Cutting mark – a mark produced along the edge as a surface is cut

• Indentation mark – a mark or impression made by a tool on a softer surface

• Impressions of other kinds, such as shoe, tire, or fabric, may be important evidence

• Before any impression is moved or otherwise handled, it must be photographed (including scale) to show all the observable details of the impression

• If the impression is on a readily recoverable item, such as glass, paper, or floor tile, the evidence is transported intact to the laboratory

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Other Impressions

• If the surface cannot be submitted to the laboratory, the investigator may be able to preserve the impression in a manner similar to lifting a fingerprint

• When shoe and tire marks are impressed into soft earth at a crime scene, their preservation is best accomplished by photography and casting

• In areas where a bloody footwear impression is very faint or where the subject has tracked through blood, leaving a trail of bloody impressions, chemical enhancement can visualize latent or nearly

invisible blood impressions

Other Impressions (continued)

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IMPRESSIONS

Class characteristics— manufacturer, type, model, size

Individual characteristics— wear patterns, nicks, marks, occlusions (like pebbles or sticks)

Shoeprints

IMPRESSIONS, CONTINUED

Shoeprints

Captured by oblique-angle photography or chemical enhancement; also by casting in soil, or lifting.

IMPRESSIONS

Treated much the same as shoeprints

Class characteristics involve design, size, type, and model.

Wear and damage cause defects that can lead to individualization.

Tire Treads

IMPRESSIONS, CONTINUED

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.

Bite Marks

IMPRESSIONS, CONTINUED

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

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

MUST BE HANDWRITTEN!!!!