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 GSR containing nitrates can stick to the person holding the firearm and leave evidence on the shooter ID: 170662
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Slide1
BALLISTICS
Gunshot Residue (GSR); Wounds and TrajectorySlide2
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 shooterSlide3
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 gasesSlide4
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 removalSlide5
GSR Testing
Thin Layer Chromatography
Gas ChromatographySlide6
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 skinSlide7
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)Slide8
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.Slide9
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 bodySlide10
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 projectileSlide11
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 10
o
, from the horizon, at what height was the bullet fired?
Law of Tangents!
Tan of Trajectory Angle = height/distancetan 10
o
= height/60 ft.
.176 = height/60 ft.
height = 10.56 ft. = 11 ft.
The bullet was fired 15 ft. above the ground.