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Forensic Analysis of Gunshot Wounds

Understand gunshot wound mechanisms and patterns, X-ray significance, implications for suicides, detection of gunshot residue, clothing distance determinations, and more.

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Forensic Analysis of Gunshot Wounds

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  1. Gunshot Wounds

  2. Tissue Disruption • Two Principle Mechanisms • Low velocity • High velocity

  3. Low Velocity Tissue Disruption Direct laceration of the tissues (drilling effect). • Causes the permanent cavity seen at autopsy • Used to follow path of bullet

  4. High Velocity Tissue Disruption There is an additional effect of temporary cavity formation • Cavity maybe 30x the diameter of the projectile • Has a lifespan of 5 to 10 milli-seconds • Organs which are dense and inelastic may burst. Ex. - liver • Wounds of the head produce bursting injuries of the skull

  5. Shot in Skull

  6. Other Wounding Mechanisms • Shockwaves from the projectile may cause the rupture of gas filled organs. Ex-bowel • Secondary projectiles. Ex. - bone fragments or bullet fragments

  7. Ammunition Type & Wound Patterns • Full Metal Jacket • Partial or No Metal Jacket

  8. Full Metal Jacket Wound Patterns • Military style ammunition • Lead bullets jacketed with harder metal (copper) • Passes through the body and exits

  9. Partial or No Metal Jacket Wound Patterns • Lead bullets • Deforms as passing through the body

  10. X-Rays for Gunshot Wounds X-rays should always be performed in GSW • Is the projectile present? • If present, where is it located? • If the projectile exited, are fragments present and where are they? • What type of ammunition or weapon was used? • What was the path of the projectile?

  11. X-Rays

  12. Gunshot Suicide • The majority of suicides do not leave notes • A contact wound creates a presumption of suicide not accident • Suicide by multiple gunshot is uncommon but not rare • A suicide victim may test fire the weapon • In about 20% of suicides the weapon is found clutched in the hand

  13. Gunshot Suicide Contact Wound

  14. Gunshot Suicide Wound Distribution

  15. Gunshot Suicide Wound Location • An unusual location raises the presumption of homicide • Occasionally blood spatter will be deposited on the hands firing or steadying the gun

  16. GUN SHOT RESIDUE

  17. What is Gun Shot Residue? • Tiny particles of primer and gunpowder (GSR) are expelled when the gun is fired • Not water soluble • Can be dislodged by blood or rough handling

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

  19. 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

  20. How is GSR detected? GSR Chemical Tests The Griess Test

  21. How is GSR detected? GSR Chemical Tests • Sodium Rhodizonate Test • Determines if lead residues are present on the exhibit.

  22. 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

  23. 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 • Most labs will not test samples collected more than 6 hours after the shooting • Shooter’s hands are bagged

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

  25. Can GSR Convict Someone? • FBI is no longer analyzing gunshot residue • Could become a weapon for defense attorneys in pending cases and in efforts to overturn convictions

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

  27. Clothing Distance Determinations

  28. Clothing Distance Determinations • Exit Holes: • Usually provide no evidence • Usually wider than the actual diameter of the bullet

  29. GSR Deposits • The further gunshot residues travel from the muzzle, the broader and less concentrated the pattern becomes. 

  30. 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

  31. 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

  32. GSR Distance Standards

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

  34. FUN! • Go to www.firearmsid.com • Scroll over “Classroom” • Click on Student Login • Login Key: C18798Forensics08 • Full Name: Your’s & Partner’s names • Click on Cartridge Case ID-VCM

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