Presentation on theme: "Firearms Forensic analysis is vital to solve a crime that uses a gun."— Presentation transcript:
1 Firearms Forensic analysis is vital to solve a crime that uses a gun. In 2004, there were 12,00 homicides in the USThe vast majority ofU.S. homicides involveguns. And they are morepowerful than ever.Lansing State Journal, July 2007
2 Firearms: A Quick History Almost every gun is based on the same simple concept: You apply explosive pressure behind a projectile to launch it down a barrel.The earliest & simplest application of this idea is the cannon.The 1st handheld guns were essentially mini-cannons; you loaded some gunpowder & a steel ball & lit a fuse
3 War typically resulted in the need for improved weapons technology. In the late 1800’s, the revolver quickly became popular due to it’s size & quick loading.It only had to be reloaded every 5-6 shots instead of after each shot.
4 Handguns reigned supreme for the past 200 years & to this day, remain the most popular & readily available firearm.
5 Types of Firearms Handguns (pistols) Revolver Semiautomatic Rifles ShotgunsAir or BB guns
7 Bullets Made of lead, sometimes jacketed with brass, copper, or steel Bullet size—diameter (caliber or gauge)Shapes
8 Firearms Identification Often confused with the term ballisticsBallistics is the study of a projectile in motion.Inside the firearmAfter it leaves the firearmWhen it impacts the targetIdentification of Firearms is based upon this basic idea: A harder object marks a softer one & imparts/transfers its microscopic irregularities to that object.
9 Forensic Firearms Expert Did a suspect use this gun to kill that person?Did these bullets come from that gun?Was it really self-defense?Is this a case of suicide, or is foul play involved?Bullet ComparisonWeapons FunctionIs it safe? Has it been modified?Serial Number RestorationGunpowder Residue Detectionon clothes, hands, & woundsMuzzle-to-Target Distances
10 Pulling the Trigger Pulling the trigger releases the firing pin… The firing pin strikes the primer…The primer ignites the gun powder…The powder generates gas that propels the bullet forward through the barrel & ejects the spent cartridge case.
20 Bullet ComparisonsEach gun leaves distinct markings on a bullet passing through it.A gun barrel is made from a solid bar of steel that has been drilled/hallowed out.The drill leaves microscopic marks on the barrel’s inner surface.Gun manufacturers also add spiral grooves to the barrel. This is known as rifling.Lands: the space between the grooves.As a spinning bullet passes through the barrel, it is marked by these grooves.
21 RiflingThe grooved spirals inside the barrel of a gun that produce lands and grooves on a bulletLands & grooves are class characteristics
22 Striae Scratches on a fired bullet, like a barcode Can serve as individual evidenceMatching bullets or bullet to a firearm
23 Class Characteristics Class Characteristics: Once a manufacturer chooses a rifling process, for a particular class of weapon, they keep it consistent.Lands & Grooves are the same for a model..32 caliber Smith & Wesson has 5 lands & grooves twisting to the right..32 caliber Colt has 6 lands & grooves twisting to the left.Class characteristics can eliminate certain makes but are not enough to ID a particular gun.
24 Individual Characteristics Imperfections in the manufacturing process make each barrel unique.Rifled barrels, even if made in succession will NOT have identical striation (scratch-like marks).
25 Bullet ComparisonsTo match bullets to a gun, test bullets must be fired through a suspect barrel for comparison.Goddard & Comparison MicroscopesExamined bullets side-by-side (to match striated markings).
26 Cartridge Case Head Stamps Rimfire & Centerfire Cartridges Usually brass or nickel-clad brassClass evidenceManufacturerShapeCaliberCompositionHead Stamps Rimfire & Centerfire Cartridges
27 Cartridge MarkingsAll moving components contact the cartridge rather than the bullet can leave useful impressions on shell cartridges.Cartridge Case Individual Characteristics:Breech face marksFiring pin impressionsChamber marksExtractor marksEjector marks
29 Breech MarksWhen a cartridge is fired, the explosion forces the bullet down the barrel and the shell casing is forced back against the breech.This leaves impressions unique to the individual gun’s breech on the shell casing.
32 Firing Pin MarksIn order to fire the cartridge, the primer must first be ignited. To accomplish this a firing pin strikes the center ring of the cartridge.This will in turn leave a distinct impression that is unique to the firing pin of that particular gun.
38 Extracting Pin & Ejector Marks The extracting pin and ejector throw the spent shell casing from the chamber of the gun.These leave marks on the shell casing that are unique to those parts on that particular firearm.
39 Other Factors Perfect matches sometimes difficult b/c: Presence of grit & rust in a barrelRecovered bullets too mutilated or distorted on impactA spent bullet’s weight can sometimes determine the gun make.Microgrooves: 8-24 grooves; it’s not as commonGeneral Rifling Characteristics FileFBI database of known land/groove width for all weapons.
40 Shotguns Smooth barrel Projectile NOT marked as it passes throughFire small lead balls or pellets contained within a shell.Characterized by:diameter of the shotsize & shape of the wadGauge: diameter of the barrel( gauge diameter)Identification can still be made by comparison of extractor/ejector markings on shotgun shell.
42 Firearms Evidence Individual: Striae Firing pin marks Breech marks Extractor marksEjector marksChamber marksClass:Bullet typeBullet caliberBullet weightLands and groovesRiflingCartridge caseHead stamp
43 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.
44 Gunpowder Chemistry GSR Sources: victim, clothing or target shooter’s handsGunpowder ChemistryMajor detectable elements are: lead (Pb), barium (Ba) & antimony (Sb)Virtually all cartridge cases are made of brass (copper & zinc); also detectable.
45 Griess TestTests for the presence of nitrates (partially burned or unburned gunpowder)Swab of shooter’s handMust produce a pattern for a distance determination
46 Results of GSR Hand Test Negative results may be caused by:Washing the handsShooter may have been wearing glovesLead free ammunitionA rifle or shotgun may not deposit GSR on hands
52 Contact Gunshot wound This is a contact gunshot entrance wound. Since the barrel contacts the skin, the gases released by the fired round go into the subcutaneous tissue & cause the star-shaped laceration.
53 Abrasion RingThe abrasion ring, and a very clear muzzle imprint, are seen in this contact range gunshot wound.An abrasion ring, formed when the force of the gases entering below the skin blow the skin surface back against the muzzle of the gun, is seen here in this contact range gunshot wound to the right temple.
54 Entrance/Exit WoundsDisplayed here is an entrance at the left and an exit at the right.Exit wounds vary considerably in size and shape because the bullet can be deformed in its transit through the body.There may be no exit wound at all if the bullet's energy is absorbed by the tissues. Some bullets (such a a "hollowpoint") are designed to deform so that all their energy will be converted to tissue damage and not exit.This is a contact range gunshot entrance wound with grey-black discoloration from the burned powder.
55 Powder tattooing is seen in this intermediate range gunshot wound Powder tattooing is seen in this intermediate range gunshot wound. The actual entrance site is somewhat irregular, because the bullet can tumble in flight.
56 The surface of the skull demonstrates the heavy soot in this contact range entrance wound, as well as radiating fracture lines. The direction of fire was thus toward the back of this picture.
60 SERIAL NUMBER RESTORATION When a serial number is stamped into a gun, the metal underneath the number is compressed & hardened.If the number is filed-off, the hardened area may still be present.By using an acid solution the metal can be slowly eaten away.In this process the softer metal will be eaten away first and the number may reappear.
61 FIREARMS EVIDENCE COLLECTION Make sure it is unloaded!!!!!DO NOT put a pencil into a barrelREVOLVERSIndicate location of fired & unfired ammunitionAUTOMATICSCheck magazine for number of roundsFingerprint magazinePlace ID tag on trigger guard
62 AMMUNITION Write on base or nose Package in pill box or envelope Wrap in tissue to protect
63 Protect & preserve any residue Air dry if wet CLOTHINGProtect & preserve any residueAir dry if wetPackage separately in paper bagsEstablish CHAIN OF CUSTODY
64 Toolmarks Tools often used in burglaries may leave a mark. Class characteristics: type, size, shapeIndividual characteristics: features from wear and damage
65 TOOL MARK IMPRESSIONSImpressionsCutsGougesAbrasions
66 TOOL MARK IMPRESSIONS COLLECTION SUBMIT ENTIRE OBJECTPACKAGE SEPARATELY (ALWAYS!)DO NOT ATTEMPT TO FIT THE TOOL INTO THE TOOL MARK
67 Matching ToolmarksPhotography & casting are important to match tool with mark??
73 Impressions Shoeprints Class characteristics— manufacturer, type, model, sizeIndividual characteristics— wear patterns, nicks, marks, occlusions (like pebbles or sticks)
74 Captured by oblique-angle photography or chemical enhancement casting in soillifting.
75 Treated much the same as shoeprints Tire marksTreated much the same as shoeprintsClass characteristics involve design, size, type, and model.Wear and damage cause defects that can lead to individualization.TreadMate is a database containing data on more than 5,000 vehicle tires and tread patterns.Tire Treads
76 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.
77 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
78 Forensics: DebateBoth Sides of the Issue; Gun Control LawsShould gun sales and ownership be subject to federal regulation?IntroductionPro/con sidesAssertionEvidencePersonal opinion