2Lesson 1 – FirearmsLesson 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
3Forensic analysis is vital to solve a crime that uses a gun. FirearmsForensic analysis is vital to solve a crime that uses a gun.The vast majority ofU.S. homicides involveguns. And they are morepowerful than ever.Lansing State Journal, July 2007In 2004, there were 12,000 homicides in the United States.Forensic Firearm Examiner
4Types of Firearms Handguns (pistols) Rifles Shotguns Air or BB guns RevolverSemiautomaticRiflesShotgunsAir or BB guns
5Handgun Designed to be held and fired with one hand Firearms Revolver Semiautomatic pistol
6Revolver Hammer pulled back manually or when trigger is pulled FirearmsRevolverHammerBulletsHammer pulled back manually or when trigger is pulledHammer hits back of bullet casing; causes explosionBarrel rifledTrigger
7Semiautomatic pistol Hammer strikes bullet case when trigger pulled FirearmsSemiautomatic pistolBulletsHammerHammer strikes bullet case when trigger pulledBullet casing automatically ejected.Barrel rifledTrigger
8Rifle Hammer strikes bullet case when trigger pulled FirearmsRifleHammer strikes bullet case when trigger pulledBulletsBulletsHammerBullet casing manually or automatically ejected.Barrel rifled; fires bulletTrigger
9Shotgun Hammer strikes shotshell when trigger pulled FirearmsShotgunProjectileHammer strikes shotshell when trigger pulledBullet casing manually or automatically ejected.Barrel smooth; fires shot or slugTrigger
10Cartridge case Primer Propellant Projectile AmmunitionComponents:Cartridge casePrimerPropellantProjectile
11Made of lead, sometimes jacketed with brass, copper, or steel BulletsMade of lead, sometimes jacketed with brass, copper, or steelBullet size—diameter (caliber or gauge)Shapes
12RiflingThe grooved spirals inside the barrel of a gun that produce lands and grooves on a bulletLands and grooves are class characteristics.
13Types of Barrels Smooth Barrel: Hollow tube FirearmsTypes of BarrelsSmooth Barrel: Hollow tubeRifled Barrel: Barrel of gun can be rifled to put spin on bullet; increases accuracy
14Rifled Barrel Inside of barrel has hills (lands) and valleys (grooves) FirearmsRifled BarrelLandsInside of barrel has hills (lands) and valleys (grooves)Lands and grooves twist down length of gunGrooves
15Rifled Barrel (manufacturing) FirearmsRifled Barrel (manufacturing)Begin with a hollow tubeLands and grooves made by forcing cutting tools through the tube.
16Rifled Barrel (manufacturing) FirearmsRifled Barrel (manufacturing)The minor differences in manufacturing leads to differences in the scratches (striations) on the fired bullet.
17Scratches on a fired bullet, like a barcode, StriaeScratches on a fired bullet, like a barcode,that can serve as individual evidence, matching bullets or bullet to a firearm
18Usually brass or nickel-clad brass Cartridge CaseUsually brass or nickel-clad brassHead stampsRimfire and centerfire cartridgesClass evidence
19Cartridge Case, continued Individual characteristicsFiring pin marksExtractor marksBreech marks
21Firearms Evidence Individual: Class: Striae Firing pin marks Breech marksExtractor marksEjector marksChamber marksClass:Bullet typeBullet caliberBullet weightLands and groovesRiflingCartridge caseHead stamp
22Gunshot Residue (GSR) When a weapon is fired: Primer and propellant particles blow back toward the shooter.Combustion products (mostly NO2-), unburned propellant, andparticles of lead follow the bullet, spreading out with distance.
23Distance to TargetThe Greiss test converts nitrites to an orange-red color.Sodium rhodizonate reacts with traces of lead to makepurple spots.
24Forensics: Debate Both Sides of the Issue; Gun Control Laws Should gun sales and ownership be subject to federal regulation?IntroductionPro/con sidesAssertionEvidencePersonal opinion
25Lesson 2 - Toolmarks Lesson Essential Questions: How are toolmarks distinguished from one another?Vocabulary: toolmarks
26Tools often used in burglaries may leave a mark. ToolmarksTools often used in burglaries may leave a mark.Class characteristics: type, size, shapeIndividual characteristics: features from wear and damage
27Lab Activity: Matching Toolmarks ??Photography and casting are important to match tool with mark.
28Lesson 3 - Impressions Lesson Essential Questions: How are impressions used in forensic science?Vocabulary: outsoles, gait, wheelbase, stance
293 Main Types of Impressions 1. Footwear marks or shoeprints2. Tire Treads3. Bite marks
31Impressions, continued ShoeprintsCaptured by oblique-angle photography or chemical enhancement; also by casting in soil, or lifting.
32Impressions, continued Treated much the same as shoeprintsTire TreadsClass characteristics involve design, size, type, and model.Wear and damage cause defects that can lead to individualization.
33Impressions, continued Tire TreadsTreadMate is a database containing data on more than 5,000 vehicle tires and tread patterns.
34Impressions, continued Bite MarksResult from assault or sexual attack, common in domestic violenceIndividual evidence, if enough impressionsBite marks were the prime evidence in the conviction of serial killer Ted Bundy.
35Impressions, continued Serial NumbersRestoration of serial numbersItems 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