Gunshot Wound Interpretation Identification and classification of gunshot wounds

Typical Gunshot Wound Morphology

Analysis of Projectile Wounds Variability of ammunition and firearms and their effect in bone should make us cautious during interpretation and descriptions should be in general terms

WOUND TYPES PENETRATING - the bullet enters the body but does not exit (entrance wound only) PERFORATING - the bullet enters and exits the body (entrance and exit wounds)

Wipe Bullet holes of entrance in the skin might have a grey coloration to the abrasion ring. More typical in clothing (called bullet wipe) It consists of soot deposited on the surface of the bullet as it moves through the barrel NOT same as powder soot present in contact wounds

Powder Soot Comes out from the muzzle, produced by combustion of gunpowder that vaporized metals from the primer, bullet and cartridge. It embeds in tight contact wounds marking it black, cannot be washed off. In loose contact it can. Distance increases the stained area

Powder Tattooing Diagnostic of intermediate range wounds when shown individually. Powder grains do not have time to disperse and mark the skin (they are not powder burns, but rather punctuate abrasions) (Not the same as powder soot) They are numerous reddish-brown to orange-red punctures surrounding the entrance wound

CLASSIFICATIONS OF GSW (range of fire) CONTACT - muzzle is in full contact with the skin at time of discharge They maybe hard, loose, angled, or incomplete.

Contact: bulb of percussion creating larger exit hole, powder and smoke deposited into wound, stellate scarring stellation of tissues, scorching, tissue delamination, bruising by firearm part, powder in wound track, tissue blowback onto firearm, gas damage from high velocity firearms.

CLASSIFICATIONS OF GSW NEAR CONTACT - muzzle not physically touching the skin, but within 10 mm Powder grains emerging from the muzzle do not have chance to disperse and mark the skin, producing powder tattooing (not individual grains) Entrance wound surrounded by a wide zone of powder soot overlying seared, blackened skin

Near Contact depositing smoke and powder

CLASSIFICATIONS OF GSW INTERMEDIATE RANGE - (GREATER THAN 10 mm) - tattooing of gunpowder is the hallmark (individual tattoo marks).

CLASSIFICATIONS OF GSW DISTANT (LONG RANGE) - only marks on skin created by perforating bullet

Caliber Determination from Entrance Wounds EXACT DETERMINATION CANNOT BE DONE size of the hole is related not only to caliber but also to the elasticity of the tissue and the location of the wound -on average min. diameter holes are about 1.1-1.35 mm bigger than caliber

Identifying Entrance and Exit Wound Trajectory of bullet seen in outward beveling of the wound Bullet “punches out” an entrance, leaving a smooth round hole and “blows out” an exit Presence of wipe also indicates direction of bullet Exit wounds are larger than entrance wounds due to two factors: spin that stabilizes the bullet no longer holds due to tissue resistance. Increasing its yaw. 2.- bullet may be deformed in its passage through body. Both conditions increase the size of the bullet as it exits the body Beveling … why?

Funnel effect

Entrance wound Skull: round wound; usually due To angle of trajectory and angle of bullet axis are Perpendicular to bone surface … what kind of Bullet would cause a round EXIT wound …? Notice: reverse beveling

Exit wound of entrance

Estimation of Sequence Locate entrance and exit wounds Distinguish radiating from concentring fx. Follow radiating fractures from beginning to end, if this fx line ends in another, this one is later in the sequence than the fx where it stops ID the entrance wound whose fx do not end in another and you have the 1st. Shot They might miss each other, impossible to Estimate sequence.

Atypical Gunshot Wound Morphology

Keyhole entrance wound

Keyhole Defects Occurs when the bullet strikes the skull at an angle, splitting into two or more fragments Produced an entrance wound that is externally beveled Possible to infer direction of fire: the round part of the defect with inward beveling points to the placement of the weapon at time of fire. Entrance and exit wound in one

Shored Exits Changes to the exit wound which could mimic the appearance of an entrance wound Exit wounds with abraded margins (which is typical of entrance wounds). Occurs when a firm surface (or tight garments) is at site of exit the bullet everts the skin which in turn impacts against the firm surface abrading the area everted.

Interposed GSW Occurs when the bullet passes through another object (glass –stippling- ), car door) before entering the victim Frequently seen in drive-by shootings Differentiated from ricochets or deflected bullets Bullet no longer follows predictable trajectory and loses kinetic energy with first contact

Morphology of Shotgun Wounds Differences in projectiles and gas combustion Soot/wipe deposit differs from hand guns/rifles

External Ballistics

THREE MAJOR FACTORS 1) VELOCITY 2) DISTANCE 3) TISSUE TYPE

TERMINAL BALLISTICS When a bullet passes through a body, it transfers its kinetic energy to the surrounding tissue, creating a temporary cavity and a permanent wound track

CAVITATION The temporary expansion of tissues as the result of the transfer of energy from the bullet to the tissues Amount of cavitation is dependent on 1) energy, size and type of bullet, 2) elasticity of tissue, 3) distance and velocity 2 types of cavitation: permanent which roughly equals diameter of projectile Temporary greater pressure around the permanent cavity …. Which can Fx bone w/o touching it.

WEAPON VELOCITY Since the amount of damage caused by the bullet is due to the transfer of kinetic energy - the higher the velocity, the greater the damage PISTOLS <DAMAGE> HIGH-POWER RIFLES

VELOCITY/TISSUE TYPES/DISTANCE The severity of the wound is directly related to the amount of kinetic energy lost in the tissue, not the total energy possessed by the bullet (VJM DiMaio, 1985)

High Velocity Weapons More prone to produce concentric and radiating fx., And catastrophic shattering of the skull

Projectile Vs. Shrapnel Projectile: object expelled under explosive pressure (bullet) Shrapnel: explosive force fragments object and produces airborne debris

Notice radiating fractures. Originate from point of impact and moved outwards on any direction, especially weak areas, Might encounter other fx or sutures where they will dissipate their force Concentring fx: part of a circle where Centre is point of impact. Created by Intracranial pressure created by Bullet. Can occur in same injury, later in the Sequence will stop at radiating Fx. Direction of fire?