Forensic Examination of Glass

Discovered in 5000 B.C., glass used to be reserved for only the wealthiest of families or churches.  However, with the rapid expansion of glass making capabilities, glass can now be found in almost every aspect of human life.  From automobile headlights to window panes, forensic scientists are forever challenged in collecting and identifying its sources.  Other advances such as the use of refractive index and physical density have aided in the identification process, however, due to mass production capabilities, near absolute identification may be impossible. 

When Robert Henry Dale hit and killed a young girl in a crosswalk, he never expected for trace evidence of glass to finger him as the killer.  Unfortunately for him, Dr. Brian Gibbons had other plans.  After collecting fagments of glass from the scene, Dr. Gibbons began to piece them together, soon discovering that the particles came from an Italian Fiats headlight.  Ninety-five registered owners names were pulled from records, and after a brief investigation, Robert Henry Dale became the prime suspect.  His Italian Fiat had recently been taken to a bodyshop to have its headlight, windshield, and door mirror replaced.  Particles of glass recovered from the inside of the vehicle matched exactly to those that were recovered from the crime scene.  Robery Henry Dale was convicted of the crime and sentenced to life imprisonment.  Without the proper glass handling techiques of Dr. Gibbons, Robert Henry Dale may have never been captured.

The first step in forensic glass examination is to determine the location of collection.  Depending on the type of crime scene, glass particles may be found in the victims clothing, hair, shoes, shattered on the ground, or even inside the recovered vehicle.  It is important to remember that no matter where the samples are to be collected, each particle must be individually stored and labeled to prevent cross contamination.  If the sample is being collected from the clothing of a victim or suspect, the entire garment must be taken to preserve evidence.  Once in the lab, the garment will be shaken or hit to remove any loose particles, gathering them on a sterile surface.  If the collection will be taken from hair, the hair must be combed thoroughly to again remove any loose particles.

In cases such as breaking and entering, as much as thirty-percent of the glass fragments will not travel in the direction of the blow, but instead towards the perpetrator.  These fragments may take position in the clothing, and even dry-cleaning will not remove the smallest of particles.  Because of this, forensic examiners may still be able to detect glass particles even after clothes have been washed.  When taking samples of glass at the scene, it is important to collect samples from different areas of the glass still remaining in the window pane.  This is because the property of glass varies depending on where the sample was taken from.  The largest possible sample of glass should also be taken from the remaining glass in the pane to enable an easier comparison.  Once all samples have been collected, the glass may now be prepped for identification.