Development of a forensic glass database system employing refractive index measurement

Abstract

Burglary and accident cases may involve glass fragments as physical evidence found at the crime scene. In forensic investigation, the purpose of glass analysis is to determine the origin of unknown glass. The common analysis of glass is physical examination which is thickness and color identification; and refractive index (RI) measurement as major examination. Currently, a compilation of refractive index (RI) or glass database on RI values of glass found in Malaysia is desirable and much needed by the forensic chemist. In this study, twenty samples of glass each from automobile glass, building glass and household glass were collected from various sources. Physical examination such as thickness and color were done to obtain preliminary information of the glass samples. The thickness of the glass for three classifications which is building, automobile and household according to enduse was in the range of 2-6 mm. For glass color, clear transparent was found to be commonly used in glass manufacturing followed by green, white, grey, blue and bronze colored glass. Determination of RI value was affected using Glass Refractive Index Measurement 3 (GRIM3) instrument. The classification of end-use types of glass by relating RI value and thickness of automobile glass showed 3 clusters corresponding to windscreen glass (1.5152 – 1.5225), rear screen glass (1.5147- 1.5217) and side window glass (1.5188-1.5190), all samples with thickness of between 2 – 6 mm. While, building glass can be classified into heat absorbing float (1.5197 – 1. 5211), clear float (1.5189 – 1.5213), figured float (1.5164 – 1.5234) and reflective float (1.5167 - 1.5188) with sample thicknesses of 2 – 6 mm. Household glass can be classified into 2 clusters. The first cluster consisted of bulb and lamp cover glasses with thickness of between 2 - 4 mm and covered a wide RI range of 1.5133 – 1.5244 while the second cluster is comprised of bottles and decorative glasses that covered a small RI range of 1.5200 – 1.5218 and larger glass thickness of between 4 – 5 mm. All informations obtained in glass analysis were used for forensic glass database. It was developed using Microsoft SQL Server Management 2008 and Microsoft Visual Studio 2008. My Forensic Glass Database System version 2011 contained 60 records of glass. It used the thickness, colors and RI values of a glass fragments to match with those stored in the database.