Forensic glass analysis
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Glass evidence in case work
Glass analysis is applicable to a wide range of forensic cases. In burglary or rape cases, window pane may be broken and analyzed.[1] In assaults, broken glass bottles may be found and analyzed in addition to glass fragments that may remain on clothing.[1] Glass analysis is also applicable to motor vehicle crashes, particularly hit and run cases, as glass from headlights can be analyzed.[1]
Collection of glass evidence from crime scenes
Depending on the form of the evidence, glass analysis can be collected in several ways. When possible, it is preferred that the entire item of evidence, such as a glass fragment or sweater with glass shards, is collected.[2] Glass evidence can also take on the form of trace evidence. In these cases, trace evidence lifters, forensic vacuums or tweezers can aid in the collection of the glass evidence.[2] Small glass fragments or shards can be secured in a pharmacist's fold and in an envelope.[2] It is also important the the location from where the glass was recovered is noted.[1] When it is suspected that an individual has small glass fragments on their person, their hair can be combed and caught on examination paper in an attempt to recover potential glass fragments.[1] In addition to combing the hair, the individual can remove their clothes on examination paper which can then be sealed and saved for examination at a later time.[1]
Methods of analysis of glass evidence: comparative analysis
Comparative analysis
It is possible to compare multiple glass fragments using the techniques described below in order to understand if the glass fragments can be excluded as originating from the same source.
Physical match
Two glass fragments may be physically matched with one another. This may exclude the glass fragments from having originated from a different source.[3]
Refractive index
The refractive index of a glass fragment may be determined and compared with that of another another glass fragment in order to understand if they can be excluded from having originated from the same source.[3] The refractive index can be determined using immersion methods as well as automated methods.[3] Immersion methods entail the use of liquids with known refractive indices. The glass fragments are immersed in the liquids, often oils, and Becke lines are examined according to the Becke line test.[3] Automated methods entail a camera and computer which make measurements of glass fragments in varying temperatures.[3]
Density
The density of a glass fragment can be determined using a density meter.[3] The density of a glass fragment will depend on the batch characteristics and composition. Although, density is tested less frequently than refractive indices, it can be used to determine if two glass fragments more likely originated from a different source.[3]
Elemental analysis
Glass fractures: direction of force, sequence of force
References
- ^ a b c d e f Gardner, Ross M. (2021). Practical crime scene processing and investigation. Donna Krouskup (Third Edition ed.). Boca Raton. ISBN 978-1-032-09443-4. OCLC 1255870591.
{{cite book}}:|edition=has extra text (help)CS1 maint: location missing publisher (link) - ^ a b c Baxter, Everett (2015). Complete crime scene investigation handbook. Boca Raton, Florida. ISBN 978-1-4987-0144-0. OCLC 923845205.
{{cite book}}: CS1 maint: location missing publisher (link) - ^ a b c d e f g Bottrell, Maureen C. (2009-04-01). "Forensic glass comparison: background information used in data interpretation". Forensic Science Communications. 11 (2).