FIREARMS TOOLMARKS AND IMPRESSIONS. TYPES OF FIREARMS HANDGUNS (PISTOLS) REVOLVER SEMIAUTOMATIC...
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Transcript of 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!!!!