Two glass fragments, one from a broken window at a crime scene and one recovered from a suspect's shoe, are placed separately in a density gradient column. Both fragments come to rest and remain suspended at exactly the same level in the column. What does this observation establish?

• A The two fragments have identical refractive indices
• B Both fragments have the same elemental composition
• C Both fragments came from the same pane of glass
• D Both fragments have the same density ✓

Explanation

In the flotation or gradient density method a fragment sinks if denser than the surrounding liquid, rises if lighter, and stays suspended where its own density equals that of the medium. Resting at the same height therefore establishes matching densities. Density is only a class characteristic: many panes of ordinary soda-lime glass share the same density and refractive index, so individual source attribution still needs elemental profiling by methods such as ICP-MS.

Reference: Simpson's Forensic Medicine, 13th ed.

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