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Chapter15 Firearms
Chapter15 Firearms
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  2. 2. FIREARMS • Forensic analysis is vital to solving a crime that uses a gun. • In 2004, there were 12,00 homicides in the US
  3. 3. FIREARMS: A QUICK HISTORY 1. Almost every gun is based on the same simple concept: You apply explosive pressure behind a projectile to launch it down a barrel. 2. The earliest & simplest application of this idea is the cannon. 3. The 1st handheld guns were essentially mini-cannons; you loaded some gunpowder & a steel ball & lit a fuse
  4. 4. 4. War typically resulted in the need for improved weapons technology. 5. In the late 1800s, the revolver quickly became popular due to its size & quick loading. • It only had to be reloaded every 5-6 shots instead of after each shot.
  5. 5. 6. Handguns reigned supreme for the past 200 years & to this day, remain the most popular & readily available firearm.
  6. 6. TYPES OF FIREARMS 1. Handguns (pistols) – Revolver – Semiautomatic 2. Rifles 3. Shotguns 4. Air or BB guns Handgun
  7. 7. AMMUNITION Components 1. Cartridge case 2. Primer 3. Propellant 4. Projectile
  8. 8. BULLETS • Made of lead, sometimes jacketed with brass, copper, or steel • Bullet size—diameter (caliber or gauge) • Shapes
  9. 9. FIREARMS IDENTIFICATION 1. Often confused with the term ballistics 2. Ballistics is the study of a projectile in motion. • Inside the firearm • After it leaves the firearm • When it impacts the target 3. Identification of Firearms is based upon this basic idea: A harder object marks a softer one & imparts/transfers its microscopic irregularities to that object.
  10. 10. FORENSIC FIREARMS EXPERT 1. Did a suspect use this gun to kill that person? 2. Did these bullets come from that gun? 3. Was it really self-defense? 4. Is this a case of suicide, or is foul play involved? 5. Bullet Comparison 6. Weapons Function – Is it safe? Has it been modified? 7. Serial Number Restoration 8. Gunpowder Residue Detection – on clothes, hands, & wounds 9. Muzzle-to-Target Distances
  11. 11. PULLING THE TRIGGER 1. Pulling the trigger releases the firing pin… 2. The firing pin strikes the primer… 3. The primer ignites the gun powder… 4. The powder generates gas that propels the bullet forward through the barrel & ejects the spent cartridge case.
  12. 12. BULLET CALIBER 1. Caliber: the diameter of the gun barrel. 2. Caliber is recorded in • hundredths of an inch (.22 & .38) • millimeters (9mm)
  14. 14. CARTRIDGE PARTS & HOW IT WORKS Cartridge Parts and How it Works Cartridge Case Gun Powder Lead Bullet Primer
  16. 16. BULLET COMPARISONS 1. Each gun leaves distinct markings on a bullet passing through it. 2. A gun barrel is made from a solid bar of steel that has been drilled/hallowed out. 3. The drill leaves microscopic marks on the barrel’s inner surface. 4. Gun manufacturers also add spiral grooves to the barrel. This is known as rifling. 5. Lands: the space between the grooves. 6. As a spinning bullet passes through the barrel, it is marked by these grooves.
  17. 17. RIFLING 1. The grooved spirals inside the barrel of a gun that produce lands and grooves on a bullet 2. Lands & grooves are class characteristics
  18. 18. STRIAE 1. Scratches on a fired bullet, 2. like a barcode 3. Can serve as individual evidence 4. Matching bullets or bullets to a firearm Scratch
  19. 19. CLASS CHARACTERISTICS 1. Class Characteristics: Once a manufacturer chooses a rifling process, for a particular class of weapon, they keep it consistent. 2. 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. 3. Class characteristics can eliminate certain makes but are not enough to ID a particular gun.
  20. 20. INDIVIDUAL CHARACTERISTICS 1. Imperfections in the manufacturing process make each barrel unique. 2. Rifled barrels, even if made in succession will NOT have identical striation (scratch-like marks).
  21. 21. BULLET COMPARISONS 1. To match bullets to a gun, test bullets must be fired through a suspect barrel for comparison. 2. Goddard & Comparison • Examined bullets side-by-side (to match striated markings).
  22. 22. CARTRIDGE CASE 1. Usually brass or nickel-clad brass 2. Class evidence – Manufacturer – Shape – Caliber – Composition Head Stamps Rimfire & Centerfire Cartridges
  23. 23. CARTRIDGE MARKINGS 1. All moving components contact the cartridge rather than the bullet can leave useful impressions on shell cartridges. 2. Cartridge Case Individual Characteristics: • Breech face marks • Firing pin impressions • Chamber marks • Extractor marks • Ejector marks
  24. 24. Breech Extracting Pin Firing Pin Ejector (not shown)
  25. 25. BREECH MARKS When 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. Breech 1. When a cartridge is fired, the explosion forces the bullet down the barrel and the shell casing is forced back against the breech. 2. This leaves impressions unique to the individual gun’s breech on the shell casing.
  28. 28. FIRING PIN MARKS 1. In order to fire the cartridge, the primer must first be ignited. To accomplish this a firing pin strikes the center ring of the cartridge. 2. This will in turn leave a distinct impression that is unique to the firing pin of that particular gun. Firing Pin M In ca mu ac pin rin Th dis is of
  32. 32. EXTRACTING PIN & EJECTOR MARKS 1. The extracting pin and ejector throw the spent shell casing from the chamber of the gun. 2. These leave marks on the shell casing that are unique to those parts on that particular firearm. Extracting Pin and 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.
  33. 33. OTHER FACTORS 1. Perfect matches are sometimes difficult b/c: • Presence of grit & rust in a barrel • Recovered bullets too mutilated or distorted on impact 2. A spent bullet’s weight can sometimes determine the gun’s make. 3. Microgrooves: 8-24 grooves; it’s not as common 4. General Rifling Characteristics File • FBI database of known land/groove width for all weapons.
  34. 34. SHOTGUNS 1. Smooth barrel – Projectile NOT marked as it passes through 2. Fire small lead balls or pellets contained within a shell. 3. Characterized by: – diameter of the shot – size & shape of the wad – Gauge: diameter of the barrel ( gauge  diameter) 4. Identification can still be made by comparison of extractor/ejector markings on the shotgun shell.
  36. 36. FIREARMS EVIDENCE Individual: 1. Stria 2. Firing pin marks 3. Breech marks 4. Extractor marks 5. Ejector marks 6. Chamber marks Class: 1. Bullet type 2. Bullet caliber 3. Bullet weight 4. Lands and grooves 5. Rifling 6. Cartridge case 7. Head stamp
  37. 37. GUNSHOT RESIDUE (GSR) 1. 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.
  38. 38. 1. GSR Sources: • victim, clothing, or target • shooter’s hands 2. Gunpowder Chemistry • Major detectable elements are: lead (Pb), barium (Ba) & antimony (Sb) • Virtually all cartridge cases are made of brass (copper & zinc); also detectable.
  39. 39. GRIESS TEST 1. Tests for the presence of nitrates (partially burned or unburned gunpowder) 2. Swab of the shooter’s hand 3. Must produce a pattern for a distance determination • Test
  40. 40. RESULTS OF GSR HAND TEST 1. Negative results may be caused by: • Washing the hands • Shooter may have been wearing gloves • Lead-free ammunition 2. A rifle or shotgun may not deposit GSR on hands
  42. 42. 4. With contact or a very close-range gunshot wound, it is possible to have blood spatter as well as GSR on the hand of the person firing the weapon.
  43. 43. CONTACT GUNSHOT WOUND 1. This is a contact gunshot entrance wound. 1. Since the barrel contacts the skin, the gases released by the fired round go into the subcutaneous tissue & cause the star- shaped laceration.
  44. 44. ABRASION RING 1. An abrasion ring, formed when the force of the gases entering below the skin blows the skin surface back against the muzzle of the gun, is seen here in this contact range gunshot wound to the right temple. 2. The abrasion ring, and a very clear muzzle imprint, are seen in this contact range gunshot wound.
  45. 45. ENTRANCE/EXIT WOUNDS 3. This is a contact range gunshot entrance wound with grey-black discoloration from the burned powder. Displayed here is an entrance at the left and an exit at the right. 1. Exit wounds vary considerably in size and shape because the bullet can be deformed in its transit through the body. 2. There may be no exit wound at all if the bullet's energy is absorbed by the tissues. Some bullets (such as a "hollow point") are designed to deform so that all their energy will be converted to tissue damage and not exit.
  46. 46. 4. Powder tattooing is seen in this intermediate- range gunshot wound. The actual entrance site is somewhat irregular because the bullet can tumble in flight.
  47. 47. 5. 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.
  48. 48. SERIAL NUMBER RESTORATION 1. When a serial number is stamped into a gun, the metal underneath the number is compressed & hardened. 2. If the number is filed-off, the hardened area may still be present. 3. 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.
  49. 49. FIREARMS EVIDENCE COLLECTION 1. Make sure it is unloaded!!!!! 2. DO NOT put a pencil into a barrel 3. REVOLVERS • Indicate the location of fired & unfired ammunition 4. AUTOMATICS • Check the magazine for the number of rounds • Fingerprint magazine 5. Place the ID tag on the trigger guard
  50. 50. 6. AMMUNITION • Write on base or nose • Package in pill box or envelope • Wrap in tissue to protect
  51. 51. 7. CLOTHING • Protect & preserve any residue • Air dry if wet • Package separately in paper bags 8. Establish CHAIN OF CUSTODY