GUN SHOT RESIDUE

What is Gun Shot Residue? Tiny particles of primer and gunpowder (gunshot residue or GSR) are expelled from the front of the gun and from the breechblock area when the gun is fired

What is Gun Shot Residue? The further gunshot residues travel from the muzzle, the broader and less concentrated the pattern becomes.  Because the various elements included in gunshot residues are very small and lack mass they lose their energy rapidly.

How is GSR detected? Primer is generally made up of barium nitrate and antimony sulfide Most GSR detection techniques concentrate on barium and antimony Also lead

How is GSR detected? GSR Chemical Tests Griess Test. Will not interfere with later tests for lead residues Detect the presence of nitrite residues Primary test used by forensic investigators nitroglycerine

How is GSR detected? GSR Chemical Tests The Griess Test

How is GSR detected? GSR Chemical Tests Sodium Rhodizonate Test Determines if lead residues are present on the exhibit. Pink to blue is positive for lead residues

How is GSR detected? Entomology Examiners can extract GSR from the larvae that had been feasting on the body of someone involved in, or that was in proximity to a shooting

Can GSR Convict Someone? All the shooter has to do is wash his hands thoroughly, although normal human movement and activity can dislodge the particles even if he can’t get to a sink Most labs will not test samples collected more than 6 hours after the shooting Shooter’s hands are bagged

Can GSR Convict Someone? Barium and antimony can also be found in firecrackers, paint, and some industrial settings Too many other factors involved—weather (including wind), sweating skin, dry skin, putting hands in pockets, washing

Can GSR Convict Someone? The FBI is no longer analyzing gunshot residue in its investigations It could become a weapon for defense attorneys in pending cases and in efforts to overturn convictions May 26, 2006

Distance Determinations GSR on Garments

Clothing Distance Determinations Entrance Holes: Typically have very even margins Smaller in diameter than the bullet due to the elasticity of the fabric

Clothing Distance Determinations Holster, the higher the velocity – the more damage to the garment, Bullet fragments Bullets shot from an angle has an elongated hole in garment Angled grazing bullet Bullet wipe residue – lead from bullet wiped off on garment

Clothing Distance Determinations Exit Holes: Usually provide no evidence Usually wider than the actual diameter of the bullet No bullet wipe residue

GSR Deposits GSR travels 3-5 feet in most firearms At the 3-5 foot range the gunshot residues may only consist of a few trace particles At around 18-24 inches most firearms will start to deposit considerable concentrations of GSR At distances of less than 12 inches heavy concentrations of visible gunshot residues will normally be deposited Gunshot residue is normally a combination of gunpowder residues and lead residues Modern – smokeless powder

GSR Deposits GSR is not readily water soluble and clothing left exposed to the elements will not usually diminish the residue deposits Heavy bleeding & rough handling of the garment can cover up or dislodge some residues

GSR Distance Standards Made by firing the firearm, using ammunition like that used in the actual case, into witness panels that consist of  white pieces of cotton twill jean cloth Several panels will be fired into at varying distances

GSR Distance Standards

Ballistic Gelatin Used by the shooting industry to simulate soft body tissue Provides an alternative to live animal or cadaver testing.

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