| Wound features |
Now that we have some of the basics covered, let us discuss some of the gross features of a gunshot. As mentioned previously, gunshot wounds generate temporary and permanent wound cavities. The size of these cavities is primarily influenced by the density and character of the tissue affected, the size and construction of the bullet, and speed of impact.
For example, a permanent wound cavity left by a high velocity, large caliber hunting rifle will be much greater than that of a smaller 0.22 caliber rifle, which fires a smaller bullet at lower speed. Likewise, the cavity is potentially much greater when left by a bullet that fragments and greatly deforms on impact (such as hollow point) than a solid projectile that simply passes through the animal, such as a slug or buckshot.
Finally, tissue character affects the ability of a system to tolerate the force generating the temporary cavity. For example, hollow viscus organs (bowel) are more expansile and simply may be perforated, while a kidney is encapsulated (thus preventing expansion) and would be obliterated by the same projectile. Bones may fragment, creating a shower of bone shards that function as secondary projectiles. |
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Here is an example of the effect of a a large caliber bullet wound through the calvarium of a white-tailed deer. |
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Here is another version of a similar lesion in another white-tailed deer.
The different outcome could be due to differences in impact speed, bullet mass, or design of the bullet used. |
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| The many applications of these principles, and the many types of ammunition available is a much larger body of information than can be presented here. More information on the analysis of gunshot wounds can be found in Forensic References & Links. |
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Entrance & Exit Wounds |
Gunshot wounds may not be evident immediately on external examination, especially those caused by small caliber weapons. Also, detecting bullet wounds in non-human species presents obvious problems due to the presence of hair and feathers.
Some gunshot wounds bleed surprisingly little and virtually are undetectable during gross examination. For this reason, it is necessary to skin the entire carcass to document all of the wounds. Here is a good example: |
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Grossly, there is not much remarkable about this coyote's hindlimb. You may be able to discern slight blood staining just proximal to the stifle. |
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Here we have skinned the same carcass. We find both the entrance and exit wounds through the quadriceps muscle. |
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Many people are familiar with the forensic term "tattoo", which refers to the staining of skin by gunpowder that is lodged in the skin surrounding an entrance wound when a victim is shot at close range. In animals, most wounds are inflicted from a distance, with the exception of cases where a final kill shot is administered.
Blunt projectiles, such as slugs or shot may leave an abrasion ring at the entrance wound with breaking of adjacent hair or feathers. This lesion may not occur with a bullet. The “typical” bullet entrance wound is characterized by a smooth hole in the epidermic/dermis. Here are examples of two different entrance wounds. |
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| This is a Black bear shot at close range with a slug-type projectile. Note that entrance wound is very large due the blunt slug pushing through the tissue. |
Here an entrance wound from a small caliber bullet. The pointed shape of the projectile cuts through the dermis producing a relatively smaller defect. |
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The general principle that the exit wound is larger than the entrance wound may not apply to smaller ammunition that passes through the body without significant deformation such as some 0.22 caliber ammunition or shot pellets and slugs.
As high velocity rifle ammunition fragments on impact, it may leave a much larger exit wound with extensive damage and exteriorization of tissue. Also, projectiles that fragment within a body may exit in multiple locations. |
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This can occur in Sabot slugs that break in two pieces at the waist. |
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| Wound tracks |
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This mule deer is a good example of clues that may help determine the direction of a bullet's path.
Here we see the smaller entrance wound through the skin over left shoulder and a larger exit wound further caudal on the right side.
Obviously, this observation is supportive of a bullet traveling from left to right. |
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Now take a look at the left scapula of the same animal. These photos are an example of how flat bones can help us out.
As the bullet passes through the scapula's superficial surface (top photo), it leaves a relatively smooth ring.
However, as it passes out the deep surface, the bone is splintered and broken (bottom photo).
The white-tailed deer skull below illustrates the same principle. |
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| In |
Out |
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Another technique that can provide information on the trajectory of wound is radiography. On radiographs, a high velocity bullet may result in what is known as a “lead shower”, whereby the bullet fragments as it penetrates deeper into the wound. The result of this fragmentation is a conical shaped wound track.
Shotgun pellets, slugs, and muzzleloader balls do not typically result in a lead shower and remain intact. The outcome is a more cylindrical wound track as demonstrated by similarly sized entrance and exit wounds. |
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You can see by the appearance of the radiograph on top how the term "lead shower" was derived. This is a deer that has been shot in the thorax with a high velocity bullet. It is difficult to determine the trajectory of the wound track from the view, but you can imagine how a few different radiographic views would clarify the situation.
Above (bottom) is another deer that has been shot with buckshot. Note the absence of a lead shower.
One more point - never attempt to determine caliber or ammunition size based on the radiographic appearance as this method is extremely inaccurate. |
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Another use for radiographs is preliminary differentiation of shotgun pellet type.
Lead shot is more likely to be deformed during collision than steel or alloy shot, thus radiographs can suggest the make-up of the shotgun pellet used.
However, chemical analysis is necessary to confirm the use of lead pellets. |
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| Finding Projectiles |
| The use of a metal detector or whole body radiographs or fluoroscopy may be beneficial in locating metal fragments. However, even with the benefit of radiographs, locating small fragments of metal in a large carcass can be an extremely difficult task. |
| As with locating entrance and exit wounds and identifying distinguishing lesions (e.g. abrasion rings), skinning the carcass is vital to locating projectiles. As a projectile passes through a body, its kinetic energy becomes diminished. The elastic nature of the skin often catches projectiles and leaves them lodged in subcutaneous tissues, even in relatively thin-skinned species such as avians. This phenomena is observed in human forensics as well (noted in the President Kennedy assassination!). |
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Can you see the 2 bullet fragments found beneath the skin of this
coyote?
Investigators must be careful not to damage projectiles with the knife
during prosection.
This animal was shot in the back of the head. The bullets
became lodged beneath the skin after passing through the skull and brain. |
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| Collection of Projectiles |
Proper collection and preservation is vital to preserving the
valuable information that can be obtained from projectiles. Improper handling can
deface or obscure the striations present on bullets, thus making rifling mark comparisons
difficult or impossible.
Projectiles should not be collected with metal
instruments. Investigators may use their gloved fingers or plastic or rubber-tipped
forceps to gently extract metal objects from tissue. Handling of collected
projectiles should be kept to a minimum. The whole projectiles or fragments should
be washed thoroughly and allowed to air dry completely. Fluids or tissue left on
metal can lead to corrosion and deface evidence. The objects should be padded
thoroughly and stored in a manner that minimizes moisture, such as a paper envelope. |
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Here, a bullet fragment is being washed in a plastic strainer. Why is it important to be so careful with projectiles? |
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The marks
analyzed by forensic firearm experts are incredibly small and easily defaced.
Comparison of bullets requires the use of a special microscope that allows the
side-by-side comparison of bullets and cartridge casings.
Forensic firearm
investigation is a fascinating and extensive field in itself. For more information about
these specialized investigators, check out the website FirearmsID.com an Introduction to
Forensic Firearms Identification at http://www.firearmsID.com |
| Now, for some Issues in
Wildlife Gunshot Cases that are commonly encountered in forensics. |
| Issues in
Wildlife Gunshot Cases >> |
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Veterinary Forensic Pathology | Examining Gunshot Wounds 
