Glass database links splinters to suspects and crimes
The Netherlands Forensic Institute (NFI) has developed a database, together with the police, for splinters of glass. These splinters of glass may prove whether suspects of violent robberies, smash-and-grab raids or ARM gas attacks were present at one or more crime scenes.
The Netherlands Forensic Institute (NFI) and the police started building up the database nearly two years ago. By now, it contains around 150 samples of glass from around fifty cases. In three cases, this glass database has linked suspects to several crimes.
Offenders of robberies of jewellery shops, smash-and-grab raids or ARM gas attacks often have splinters of glass on their clothes or in the soles of their shoes when being arrested, for example because they smashed the glass of a display case. These splinters of glass can remain in place for months and are hardly visible with the naked eye, if at all.
Composition of glass is unique
The composition of each piece of glass is unique because of miniscule contaminants in the raw materials for making glass. By comparing the unique composition of splinters of glass found on a suspect to glass from the database, it is possible to check whether that glass originates from a crime committed earlier.
Each piece of glass has a unique composition of raw materials, although the difference are sometimes very small. These differences are caused by contaminants in the raw materials. The concentrations of these contaminants are so small that the manufacturer no longer checks them.
These distinctive characteristics differ by piece of glass, but these differences may also occur within the production process. The glass analysts of the NFI measure the concentrations of twenty elements in each piece of glass. This produces a kind of chemical fingerprint of the material.
Plasma
The equipment used to carry out this analysis is called LA-ICMPS. This equipment emits a UV beam onto the sometimes miniscule fragments of glass for approximately 25 seconds. This creates a cloud of dust that is led to plasma of as high as 8000 degrees. That is as hot as the surface of the sun. As a result of this, the cloud of dust crumbles into parts at atomic level, the smallest parts possible.
A mass filter is used to compare the proportions of the various elements in the glass, which are subsequently compared with the pieces of glass found at the crime scene or with the glass of which the data have been stored in the glass database.
Glass analysis at the NFI
Each year, the NFI carries out twenty to thirty comparative glass analyses in connection with smash-and-grab raids or ARM gas attacks, in addition to around seventy analyses in connection with crimes including burglaries, shooting incidents, and collisions.