A high powered microscope with a heated stage was used to analyse the different glass samples collected. Glass samples are compared by looking at the Refractive Index (RI) of the individual pieces of glass. Glass from two different sources will have different RIs, and so if two pieces of glass have the same RI they can be said to have originated from the same source. As most glass is mass-produced (for example, one company may make several thousand glass milk bottles) this evidence isn't as discriminatory as a fingerprint, but can still be of value to the investigation.

Calculation of the Refractive Index of a glass sample using a high powered microscope with a heated stage.

The green glass fragments found on the car-mat (Evidence number LMW-14) had an identical RI to the green glass fragments found in the living room (Evidence number LMW-1). The RI of the clear glass fragments found on the passenger's car seat (Evidence number LMW-16) was not identical to the other RIs. This indicates that the green glass fragments found in the car and those found in the living room originate from the same source.

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