Bullet wounds: skull bevelling, shot sequence and direction
THE CONTEXT
Skull defects, fracture-line relationships and the abrasion collar provide evidence about bullet passage and the sequence or direction of firing.
Skull entrance and exit defects
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At entrance, the unsupported inner table loses a cone-shaped piece of bone, creating a bevelled crater larger than the outer-table hole.
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Bone fragments may be driven into the cranial cavity, help establish the bullet track and produce short accessory tracks. Associated lacerations are usually irregular and involve the leptomeninges.
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At exit, the inner table has a punched-out opening and the outer table has a bevelled opening.
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The defect is funnel-shaped, opening in the direction of bullet travel at both entrance and exit.
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The exit wound is larger because of bullet deformity and tumbling after entry into the skull. Radiating fissured and sometimes comminuted fractures may occur.
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Asymmetry of bevelling helps assess the angle of fire. Similar appearances may occur in the sternum, pelvis, ribs, dentures and thumbnails.
Puppe's rule
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Puppe's rule helps determine the sequence when several bullets have struck the cranium and also applies to multiple blunt-force skull fractures.
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The assessment examines intersections between fracture lines or between a fracture line and a cratered lesion to determine which crack or defect formed first.
Direction from the abrasion collar
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A bullet striking at a right angle produces a circular, uniform abrasion collar because scraping is equal on all sides.
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With an angled impact, the wound itself is round, but the marginal abrasion is oval or elliptical and wider on the side from which the bullet approaches.