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BALLISTICS

BALLISTICS. Gunshot Residue (GSR); Wounds and Trajectory. Gunshot Residue. Traces of smoke and particles of unburned powder carried sideways from the firearm by the expansion of gases as the bullet is fired

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BALLISTICS

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  1. BALLISTICS Gunshot Residue (GSR); Wounds and Trajectory

  2. Gunshot Residue • Traces of smoke and particles of unburned powder carried sideways from the firearm by the expansion of gases as the bullet is fired • GSR containing nitrates can stick to the person holding the firearm and leave evidence on the shooter

  3. Amount of GSR • The amount of GSR decreases as the distance between firearm and victim increases • The distance between the weapon and the victim can be determined by examining the GSR pattern on the body of a victim or the clothing • There is generally no GSR if the weapon is in contact with the victim since there is no room for expansion of gases

  4. GSR Collection • GSR is usually collected by swabbing the hands with cotton and water, although several different mediums and solvents can be used • GSR can be removed by washing, but chemical testing can often detect residue despite the attempted removal

  5. GSR Testing • Thin Layer Chromatography • Gas Chromatography

  6. Entrance Wounds • Are generally smaller than the size of the bullet, because the skin is somewhat elastic and stretches when a bullet enters the body • If clothing is penetrated first, fibers may be embedded in the wound pointing in the direction of penetration • GSR is usually found only on entrance wounds • If the muzzle is in contact with the skin, the hot gases released from the muzzle flash may burn the skin

  7. Entrance Wounds (cont.) • Close range (to about 6 inches): • Round gunshot wound + friction-burn halo • Burn (from explosion within gun) • Dark soot that can’t be rubbed off • Stippling (from unburned gunpowder particles striking skin) • Intermediate range (to about 3 to 6 feet depending on the weapon): • Round gunshot wound + friction burn halo • Diffuse stippling (projects to about 3 feet)

  8. Entrance Wounds (cont.) • Distant: • Round gunshot wound + friction burn halo only • If stippling can be seen, its diameter around the wound is roughly the same distance that the weapon was fired.

  9. Exit Wounds • Are usually larger, because as the bullet moves through the body, it may collect and carry body tissue and bone with it • Because bullets do not travel smoothly through a victim’s body, a larger, more irregular exit wound may occur • Sometimes bullets do not exit • High-speed bullets are more likely to pass through the body • Lower caliber bullets, such as a .22, tend to lodge within the body

  10. Trajectory • The path of the propelled bullet • The angle of trajectory can be used to trace back to the shooter • It is calculated by finding two reference points along the flight path of the projectile

  11. Trajectory Problems • A car’s seat has been shot through the car’s window. The bullet hole is located four feet above the ground. The nearest building is 60 feet away along the horizon. If the trajectory angle is found to be 10o , from the horizon, at what height was the bullet fired? • Law of Tangents!Tan of Trajectory Angle = height/distance • tan 10o = height/60 ft. .176 = height/60 ft. height = 10.56 ft. = 11 ft. The bullet was fired 15 ft. above the ground.

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