Glass Fragments

Glass fragments are one the most frequently found substances at crime scenes: Criminals break windows to gain entry into buildings, hit-and-run accidents result in broken glass, and so on. Try the following activity to see how forensic scientists analyze glass fragments at a crime lab.

Materials

- jigsaw puzzle

CAUTION: Do not try this activity with actual glass fragments.

Procedure

1. Dump the jigsaw puzzle pieces onto a table or floor. Turn each piece facedown.
2. Assemble the puzzle using only the shape of the pieces as a clue, not the elements of the picture.
3. Did you find this easier or more difficult than usual?

Explanation

Forensic scientists at a crime lab use a technique called the jigsaw method to analyze glass fragments. The jigsaw method works because when glass breaks, its surface fractures unevenly. This breaking process produces unique shapes of glass that will lock only into the pieces that were next to them at the point when the glass broke, just as each piece of a jigsaw puzzle will lock only into the pieces that go next to it.

Forensic scientists use the jigsaw method of glass-fragment analysis to solve crimes. For example, investigators may wants to know whether a piece of glass found in a hit-and –run victim’s clothing matches the glass from a broken headlight of a suspect’s automobile.

As you saw in this activity, the jigsaw method is very difficult. Forensic scientists perform other tests to match glass fragments to the scene of a crime.