Glass fracture pattern analysis at a crime scene reveals radial cracks with hackle marks. The rib marks on the radial fractures are perpendicular to the glass surface on the OPPOSITE side from the impact. This follows which principle?

• A Locard's exchange principle
• B Henry's system of fingerprint classification
• C Bertillon's principle of somatometry
• D 3R rule — Radial fractures form Rib marks on the Reverse (opposite) side of impact ✓

Explanation

The 3R rule in forensic glass analysis states: Radial fractures form Rib marks on the Reverse side of the force. When an object impacts glass, tensile stress initiates radial cracks on the far (opposite) side from impact first; rib marks (curved stress lines visible on the fracture edge) therefore are perpendicular to the glass surface on the side opposite to the force. Concentric cracks have their rib marks perpendicular to the near (impact) side. This allows determination of the direction of force application even when the projectile is not recovered.

Reference: The Essentials of Forensic Medicine and Toxicology (Narayan Reddy), 34th ed.

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Written and medically reviewed by the StethoPrep medical team.