Presentation Transcript

1. Ballistics

2. The vast majority of U.S. homicides involve guns. And they are more powerful than ever. Lansing State Journal, July 2007 1998--Deaths due to handgunsUS 11,789 Germany 373Canada 151Australia 57England and Wales 54Japan 19In 2004 there were 29,569 gun deaths56 percent suicides40 homicide
3. Introduction Ballistics- is the study of bullets and firearms Firearm = a weapon, such as a gun, capable of firing a projectile using a confined explosive Questions that can be answered by analysis of ballistic evidence What type of firearm was used? What was the caliber of the bullet? How many bullets were fired? Where was the shooter standing? What was the angle of impact? Has this firearm been used in a previous crime?
4. History of Gun Powder and Firearms Gunpowder invented over 1,000 yrs ago by chinese Gunpowder is a mixture of potassium nitrate (saltpeter), charcoal, an sulfur When ignited gunpowder expands to six times its original size causing a violent explosion Matchlock –used wicks to ignite the gunpowder Flintlock Muzzle (barrel) Loaders Gunpowder and projectile packed down barrel Barrel = the long, metal tube that guides a projectile out of the firearm Muzzle = end of the barrel of a firearm Percussion Cartridge and bullet
5. Long Guns and Handguns Long Guns Rifles- fire bullets Shotguns- fire either small round pellets (shot) or a single projectile called a slug gauge = the number of lead balls matching the barrels diameter that it takes to weigh one pound Handguns Pistols- handguns that can be fired with one hand Single shot initially not as powerful and/or accurate as rifles Today, can be classified as revolvers or semiautomatics Revolvers- have a cylinder which contains several cartridges that can be fired in rapid succession Invented by Samuel Colt, patented in 1835 Cylinder can hold several cartridges Semiautomatic Hold 10 cartridges in one magazine (clip) Fire one bullet per pull of trigger The empty cartridge ejects and the next cartridge advances automatically Fully automatic Fire repeatedly as long as trigger is pressed
6. Firearms and Rifling An archer will hit a target with greater accuracy if there is a twist on the end of the arrow feathers Same applies to guns and bullets Barrel has lands and grooves Rifling = spiral pattern of lands and grooves in the barrel of a firearm Lands = raised area Grooves = indentations Lands and grooves cause bullet to spiral like a football The “rifling pattern” left on the bullet is specific to each firearm No two guns, even of same model, are rifled the same when made Provides individual evidence
7. Anatomy of a Cartridge Cartridge = a case that holds a bullet, primer powder, and gunpowder Shell Casing = the metal (usually brass) housing from the gunpower of a firearm The bullet can be composed of lead copper, or a combination of various metals Lead Lead alloy (lead mixed w/ other metals Semijacketed- thin layer of brass coating Fully jacketed-jacketed-completely covered with brass Greater penetration power The primer powder mixture initiates the contained explosion that pushes the bullet down the barrel Struck by firing pin of firearm, pressure caused ignition The anvil and flash hole provide the mechanism of delivering the explosive charge from the primer powder to the gunpowder The headstamp on the bottom of the cartridge case identifies the caliber and manufacturer
8. How a Firearm Works Pull the trigger and the firing pin of the firearm hits the base of the cartridge, igniting the primer powder mixture The tiny explosion (not much more than a spark) of the primer powder misture on the anvil delivers a spark through the flash hole to the main gunpowder suppy The main gunpowder supply ignites, and the pressure of the explosion pushes the bullet from the casing and into the barrel of the firearm. The amount of gunpowder and mass of bullet determines the speed of the bullet The bullet follows the lands and grooves pattern of the barrel and begins to spiral before it leaves the barrel
9. Caliber of the Cartridge Caliber- a measure of the inside diameter of a firearm barrel Bullets (and their cartridges) are name by caliber and length. The caliber is a measure of the diameter of the cartridge.22, .25, .357, .44, and .45 are common calibers Example .45 = 45/100 of an inch European method using metric system (example 9mm) Bullet removed from wound or crime scene can be linked to a gun by its caliber size
10. Marking on Bullets Lands and grooves rifling pattern in barrel of gun leaves a unique pattern on bullet suspected weapons can be test fired and bullets compared for individualizing evidence
11. Marks on a Spent Cartridge Marks left on bottom of cartridge by firing pins, can be analyzed Breechblock marks are produced on cartridge as it travels in opposite direction of bullet Breech is the rear part of a firearm barrel Where cartridge is loaded, opposite muzzle Cartridge hits breech block and mark is left suspected weapons can be test fired and cartridges compared for individualizing evidence Some other marks Extractor and Ejector marks Extractor – mechanism that places cartridge into chamber of firearm Ejector – mechanism that removes cartridge from chamber after firearm has fired
12. Gunshot Residues All firearms explode gunpowder and produce gunshot residue (GSR) Residues are traces of smoke and particles of unburned powder carried sideways from the firearm by the expansion of gases as the bullet is fired Gunshot residues contain nitrates and metals Residues stick to the person holding the firearm and leave evidence on the shooter The amount of GSR on the victim decreases as the distance between shooter and victim increases
13. Trajectory Trajectory is the path of the for the propelled bullet Used to determine the position of a shooter Trajectory can be calculated by finding two or more reference If ignoring gravity, it can be assumed that projectiles such as bullets travel in straight lines Reference points can be bullet holes in objects or victims An entry point and exit point on a victim Gunshot residue or spent cartridge casings Lasers can trace a straight-line path to determine the position of the shooter
14. Gravity and Trajectory Two major forces acting on a bullet after it has been fired Forward force of the gunshot and Downward force of gravity If shot from close to medium distances gravity can be negated in calculation of trajectory Gravity needs to be accounted for if shots are fired from greater distances
15. Determining Location of Shooter Building is 60 feet away along the horizon line Bullet hole is 4 feet above the ground Where is the shooter located?
16. Triangulation B is where the shooter is located; find the length of BC The Abc triangle has the same proportions as the ABC triangle So or AB = 732.3”
17. Triangulation Using Pythagorean’s theorem AB2 = AC2 + BC2 732.32 = 7202 + BC2 BC2 =732.32 – 7202 BC2 =536117 – 518400 BC = √17717 (square root) BC = 133.1 inches BC = 11.1 feet We know that the bullet hole in the seat is four feet above the ground, so the shooter is 15.1 feet above the ground
18. Sample 1 Ab = 32” Ac = 24 “ CALCULATE BC Building is 40 feet away along the horizon line Bullet hole is 4 feet above the ground
19. Sample 2 Ab = 22” Ac = 14“ Calculate BC Building is 20 feet away along the horizon line Bullet hole is 4 feet above the ground
20. Bullet Wounds Why do entrance wounds tend to be smaller than exit wounds? Bullet enters body small May pick bone and tissue as it travels through body tumbling effect If the bullet penetrates clothing, what can fibers embedded in the wound indicate? entrance vs exit wound Where is gunshot residue usually found? usually only around entrance wounds If the gun is fired with the muzzle touching the victim’s skin, what telltale mark may show up? burn mark on skin Will larger or will smaller caliber bullets tend to lodge within the body rather than passing through? Why? smaller caliber-less velocity (speed)