Trace Analysis--Glass Evidence

Trace evidence like glass fragments and paint chips can be essential clues in solving a case.

Sample material subjected to inductively-coupled plasma mass spectroscopy (ICP-MS) analysis and tests for chemical coatings on the glass surface yielded a specific profile for the glass. This was compared to the glass databases available from the FBI and car manufacturers, and indicated a high probability that the glass was from a 1980-1985 Ford.

A close friend of the victim indicated to investigators that the victim had told her she had received some unwanted calls from an old college boyfriend lately. With his name in hand, investigators determined that he had several cars, including a 1984 Ford Mustang SVO. Looking at the car in the parking lot where the suspect worked led investigators to believe that the right headlamp had recently been replaced.

Back at the trace lab again

The trace technician had completed analysis on the glass shards from the flower vase that was the murder weapon. The glass had a high lead content, and also an unusually high zinc oxide (ZnO) and strontium oxide (SrO) content. That and its fracture pattern, as well as color, density and RI allowed the lab to develop a profile for the glass.

The college boyfriend was brought in for questioning and was very uncooperative. He could not account for his whereabouts at the time of the crime, and admitted that he had several phone contacts with the victim recently. A search of his car and residence yielded glass shards similar to those from the purple flower vase from the driver-side carpet of his car. In addition, similar shards were removed from the soles of a pair of sneakers found in his closet. Further analysis of these sources also yielded traces of the victim's blood from blood spatter on the shoes and transfer blood spatter on the car seat.

At trial, the two pieces of glass trace evidence were critical parts of the prosecution's case. The members of the jury viewed these as strong circumstantial evidence.

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