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Ballistic Evidence

Ballistic Evidence

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Ballistic Evidence

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  1. Ballistic Evidence

  2. Ballistics • Ballistics  the study of bullets and firearms • Firearm  a weapon, such as a gun, capable of firing a projectile using a confined explosive

  3. Firearms History • Matchlock weapons  Relied on wicks to carry a flame to the gunpowder • Flintlock weapons Relied on sparks from a piece of flint to ignite the gunpowder • Could be used in damp weather • Percussion weapons Introduction of cartridges (a casing that holds a bullet)

  4. Gun Parts – The Barrel Barrel of a gun is produced from a single rod of steel that has been drilled through the center • Drill markings are different for each type of gun produced • IE. Shotgun barrels are different than a rifle barrel • Have different purposes • Can vary in length • No two rifled barrels, even those manufactured in succession, will have identical striation markings

  5. Barrel • Manufacturers also impress the barrel with spiral grooves  Known as rifling • The surfaces of the original bore remaining between the grooves are called lands

  6. Barrel Each gun manufacturer uses its own technique and own signature amount of lands and grooves • Ex. Smith and Wesson uses five lands and grooves twisted to the right

  7. Caliber Caliber of a rifle or handgun is the diameter of the gun barrel • Usually recorded in hundredths of an inch or in millimeters • Shotguns are measured by gauges

  8. Hammer Part of the gun that is responsible for beginning the reaction of a bullet firing is the hammer

  9. Breechblock / Ejector • Breechblock • The rear part of the firearm barrel Stops the bullet casing from flying through the back of the gun • Ejector Spits out the empty shell casings to make room for the next bullet

  10. Bullet / Ammunition Bullet is a combination of a gunpowder and a projectile • Can be a single bullet or can be hundreds of buckshot Back of the bullet contains a firing pin that once struck, ignites the gun powder

  11. Bullet

  12. How A Firearm WorksA Review • Pull the trigger and the firing pin of the firearm hits the base of the cartridge, igniting the gunpowder mixture • Gases expand and bullet is propelled forward and case is forced backward • Bullet is expelled through the barrel – spinning according to the land and groove pattern. The spent casing is ejected from the rear of the gun.

  13. Bullet projection • As soon as the explosion occurs, the bullet is expelled out through the barrel of the gun • Bullet is spinning • This is due to the lands and groves in the barrel • This creates markings on the bullet

  14. Opposite Reaction • Bullet casing is forced backwards against the breechblock • Casing is the removed via the ejector

  15. Casing Imprints • Casings are indented with the markings from the weapon’s firing and loading mechanisms: • Hammer • Breechblock • Ejector/extractor

  16. Questions to Answer • 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 the firearm been used in a previous crime?

  17. Critical Firearms Evidence • All of the items below are essential in firearms investigation • The bullet • The weapon • The serial numbers on the weapon • The gunpowder on garments, around wounds, and on hands

  18. The Weapon • Safety is of the utmost importance when collecting the weapon • When collecting a found weapon, it is best to pick it up by the edges of the trigger guard or by the checkered portion of the grip

  19. Weapon Comparison • Once a gun is collected, a test firing is completed in water to provide a point of comparison for evidence collected with the crime • Remember each weapon will leave its own unique markings on the ammunition that it is using (both bullet and casing)

  20. Weapon Serial Numbers • Each weapon has a serial number associated with it • Used for registration and purchasing reasons • Criminalists can track movement of weapons based on serial number • Most of the time, criminals try to remove the serial number • Stamped serial numbers put stress on the metal of the gun • When an etching agent is poured on area, the stressed areas dissolve faster than surrounding metal and reveal the serial number

  21. Collecting A Bullet • If a bullet is found lodged in something, it is best to remove the surrounding material as to not disturb any of the striations made • Investigator puts initials on nose or back of bullet • Wraps it in tissue paper to avoid scratching during transfer

  22. NIBIN • National Integrated Ballistics Network • Combination of NIBIS and Drugfire • United in 2000 • NIBIN networks allows ballistics identification to be conducted on a local, national, or international scale. • This networking feature has been employed to successfully link crimes between countries.

  23. Measuring Distance • In cases where a victim has suffered a gunshot wound, it is important to determine the distance from weapon to victim / identify the location of the shooter Distance is determined primarily by the presence and distribution of certain powder patterns or by the spread of a shot (for a shotgun)

  24. Gunshot Residue (GSR) Primers in the bullet contain a blend of different chemicals Look for the elements Antimony and Barium

  25. Firearm Discharge • When a firearm is discharged, unburned and partially burned particles of gunpowder (in addition to smoke) are propelled out of the barrel, along with the bullet, towards the target It is the distribution of gunpowder particles and other discharge residues around the bullet hole that permits an assessment of the distance from weapon to target

  26. Gunpowder Distribution Factors • Factors that influence gunpowder residue on the target: • Barrel length • Caliber • Type of ammunition • Type and condition of weapon fired • Distance from weapon to target • No GSR will be on target if further than 3 feet

  27. Gunshot Residue Distribution • Handling of a used firearm, the passage of time, and the resumption of normal activities following a shooting, gun shot residue is usually redistributed to other areas • Becomes harder to trace back to original weapon

  28. Bullet Wipe Dark ring around the perimeter of the entrance hole in a target • Consists of a mixture of carbon, dirt, lubricant, primer residue, and lead being wiped off of the bullet

  29. Gunshot Residue Detection • Swab both the firing and nonfiring hand with a 5% solution of nitric acid or • Use adhesive tape on the hands to pick up the particles of residue • Tape is put under scanning electron microscope • More specific than hand swabbing

  30. GSR Detection • Infrared photography – used to help find GSR in difficult situations (dark clothing or bloody clothing) • Greiss test  chemical test to develop patterns of GSR around bullet holes • Photopaper is ironed over entrance area • Paper is sprayed with chemical • Turns GSR pink then blue-violet