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Firearms, Toolmarks, and Impressions 1. 2 Lesson 1 – Firearms Lesson Essential Questions: How are firearms and bullets distinguished from one another?

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Presentation on theme: "Firearms, Toolmarks, and Impressions 1. 2 Lesson 1 – Firearms Lesson Essential Questions: How are firearms and bullets distinguished from one another?"— Presentation transcript:

1 Firearms, Toolmarks, and Impressions 1

2 2 Lesson 1 – Firearms Lesson Essential Questions: How are firearms and bullets distinguished from one another? Vocabulary: Caliber, bore, gauge, shot, slug, grains, rifled, lands, grooves, striae, cannelures, head stamp, breech, extractor, ejector, magazine, chamber

3 Firearms, Toolmarks, and Impressions 3 Forensic analysis is vital to solve a crime that uses a gun. The vast majority of U.S. homicides involve guns. And they are more powerful than ever. Lansing State Journal, July 2007 In 2004, there were 12,000 homicides in the United States. Forensic Firearm Examiner Firearms

4 Firearms, Toolmarks, and Impressions 4 Types of Firearms Handguns (pistols) Revolver Semiautomatic Rifles Shotguns Air or BB guns

5 Firearms, Toolmarks, and Impressions 5 Handgun Designed to be held and fired with one hand RevolverSemiautomatic pistol Firearms

6 Firearms, Toolmarks, and Impressions 6 Revolver Hammer pulled back manually or when trigger is pulled Hammer hits back of bullet casing; causes explosion HammerBullets Trigger Barrel rifled Firearms

7 Firearms, Toolmarks, and Impressions 7 Semiautomatic pistol Bullet casing automatically ejected. Hammer Bullets Trigger Hammer strikes bullet case when trigger pulled Barrel rifled Firearms

8 Firearms, Toolmarks, and Impressions 8 Rifle Hammer strikes bullet case when trigger pulled Bullet casing manually or automatically ejected. Bullets Trigger Bullets Hammer Barrel rifled; fires bullet Firearms

9 Firearms, Toolmarks, and Impressions 9 Shotgun Hammer strikes shotshell when trigger pulled Bullet casing manually or automatically ejected. Projectile Trigger Barrel smooth; fires shot or slug Firearms

10 Firearms, Toolmarks, and Impressions 10 Ammunition Cartridge case Primer Propellant Projectile Components:

11 Firearms, Toolmarks, and Impressions 11 Bullets Made of lead, sometimes jacketed with brass, copper, or steel Bullet sizediameter (caliber or gauge) Shapes

12 Firearms, Toolmarks, and Impressions 12 Rifling The grooved spirals inside the barrel of a gun that produce lands and grooves on a bullet Lands and grooves are class characteristics.

13 Firearms, Toolmarks, and Impressions 13 Smooth Barrel: Hollow tube Firearms Types of Barrels Rifled Barrel: Barrel of gun can be rifled to put spin on bullet; increases accuracy

14 Firearms, Toolmarks, and Impressions 14 Rifled Barrel Inside of barrel has hills (lands) and valleys (grooves) Lands Grooves Lands and grooves twist down length of gun Firearms

15 Firearms, Toolmarks, and Impressions 15 Rifled Barrel (manufacturing) Begin with a hollow tube Lands and grooves made by forcing cutting tools through the tube. Firearms

16 Firearms, Toolmarks, and Impressions 16 Rifled Barrel (manufacturing) The minor differences in manufacturing leads to differences in the scratches (striations) on the fired bullet. Firearms

17 Firearms, Toolmarks, and Impressions 17 Striae Scratches on a fired bullet, like a barcode, that can serve as individual evidence, matching bullets or bullet to a firearm

18 Firearms, Toolmarks, and Impressions 18 Cartridge Case Usually brass or nickel-clad brass Head stamps Rimfire and centerfire cartridges Class evidence

19 Firearms, Toolmarks, and Impressions 19 Cartridge Case, continued Individual characteristics Firing pin marks Breech marks Extractor marks

20 Firearms, Toolmarks, and Impressions 20 Features of a Semiautomatic Handgun

21 Firearms, Toolmarks, and Impressions 21 Firearms Evidence Individual: Striae Firing pin marks Breech marks Extractor marks Ejector marks Chamber marks Class: Bullet type Bullet caliber Bullet weight Lands and grooves Rifling Cartridge case Head stamp

22 Firearms, Toolmarks, and Impressions 22 Gunshot Residue (GSR) When a weapon is fired: Primer and propellant particles blow back toward the shooter. Combustion products (mostly NO 2 - ), unburned propellant, and particles of lead follow the bullet, spreading out with distance.

23 Firearms, Toolmarks, and Impressions 23 Distance to Target The Greiss test converts nitrites to an orange-red color. Sodium rhodizonate reacts with traces of lead to make purple spots.

24 Firearms, Toolmarks, and Impressions 24 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

25 Firearms, Toolmarks, and Impressions 25 Lesson 2 - Toolmarks Lesson Essential Questions: How are toolmarks distinguished from one another? Vocabulary: toolmarks

26 Firearms, Toolmarks, and Impressions 26 Toolmarks Class characteristics: type, size, shape Individual characteristics: features from wear and damage Tools often used in burglaries may leave a mark.

27 Firearms, Toolmarks, and Impressions 27 Lab Activity: Matching Toolmarks ? ? Photography and casting are important to match tool with mark.

28 Firearms, Toolmarks, and Impressions 28 Lesson 3 - Impressions Lesson Essential Questions: How are impressions used in forensic science? Vocabulary: outsoles, gait, wheelbase, stance

29 Firearms, Toolmarks, and Impressions 29 3 Main Types of Impressions 1. Footwear marks or shoeprints 2. Tire Treads 3. Bite marks

30 Firearms, Toolmarks, and Impressions 30 Impressions Class characteristics manufacturer, type, model, size Individual characteristics wear patterns, nicks, marks, occlusions (like pebbles or sticks) Shoeprints

31 Firearms, Toolmarks, and Impressions 31 Impressions, continued Shoeprints Captured by oblique-angle photography or chemical enhancement; also by casting in soil, or lifting.

32 Firearms, Toolmarks, and Impressions 32 Impressions, continued 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

33 Firearms, Toolmarks, and Impressions 33 Impressions, continued TreadMate is a database containing data on more than 5,000 vehicle tires and tread patterns. Tire Treads

34 Firearms, Toolmarks, and Impressions 34 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

35 Firearms, Toolmarks, and Impressions 35 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-CuCl 2


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