Determining the type of glass gives investigators evidence that is considered to have class characteristics. Only in cases where the suspect fragments exactly match fragments from the crime scene is it possible to consider this type of evidence as showing individual characteristics that point to a specific source.
How is glass evidence useful in a forensic investigation?
7) Glass evidence can be useful in a forensic investigation because it can identify matches on the victim, suspect, and scene. Although it is considered class evidence, it can contain pieces of individual evidence such as blood, hair, and fingerprints that could lead to a specific source.
How to identify different samples of glass?
Basic properties, such as color, thickness, and curvature, can also help to identify different samples of glass just by looking at them. Optical properties, such as refractive index (RI), are defined by various manufacturing methods. RI is the manner in which light passes through the glass.
What is the use of glass in construction?
Glass is a unique and extremely versatile material that can be engineered to exhibit specific optical, thermal, chemical, and mechanical properties. As a result of its exceptional engineering properties – transparency, strength, workability, transmittance and u value, glass has been heavily used in the construction industry.
What is glass analysis in a crime scene?
Glass Analysis. Trace evidence can be found at a crime scene in a number of different forms, including hairs and fibers, glass, or soil. Glass analysis includes determining the type of glass based on glass fragments. However, the entire fractured pane or window can be helpful when determining direction and sequence of force.
What is the importance of glass as evidence in forensic science?
Purpose The value of glass fragments as evidence is not always fully recognized. Windows, automobile glass, broken bottles, and other glass objects may be crucial evidence in burglary, murder, hit-and-run and many other types of crime.
Why is it important to analyze glass?
Glass analysis can be helpful in various ways. Glass fragments at a crime scene should always be collected and analyzed because several clues can be gathered about the events that occurred during the crime. Fragments of glass from headlights at a hit-and-run scene can leave clues about the unknown vehicle.
What is the significance of determining the types of glass fractures?
The study of fracture pattern of glass has been of long interest to the forensic community. The glass fracture pattern analysis is very useful to establish the sequence of events and to link together items of evidence and it is of paramount importance in such cases where firearm is used.
Why is glass useful in a crime scene investigation?
The value of glass as "evidentiary material" lies in its inherent characteristics such as: (a) it is a fragile material that is often broken and hence commonly found in various types of crime scenes, (b) it can be easily transferred from the broken source to the scene, suspect, and/or victim, (c) it is relatively ...
How glass can be used as evidence?
Glass - Glass can be used to gather evidence, for example collecting fingerprints or blood from a broken window; however, glass also has a place in the trace evidence section. Broken glass fragments can be very small and lodge in shoes, clothing, hair or skin.
How can glass analysis help determine a sequence of events?
By looking closely at the glass, the direction of impact can also be determined. When more than one fracture is present, it is possible to determine the sequence in which the breaks occurred.
How can an investigator differentiate one glass sample from another?
Comparing the color of a suspect piece of glass with the color of a reference sample can distinguish whether the two samples share a common source. As a consequence, significant color differences between glass fragments can be used as the basis for exclusion of a suspect.
What are three characteristics of glass that could be used to match glass from a crime scene to a suspect?
26 Cards in this SetThe value of trace forensic evidence was first recognized by __________ in _____.Edmund Locard 1910Glass What are three characteristics of glass that could be used to match glass from a crime scene to a suspect?color Thickness Chemical composition24 more rows
What are the two most important physical properties of glass for forensic comparisons?
To compare glass fragments, a forensic scientist evaluates two important physical properties: density and refractive index.
Why is it important to collect all the glass from a scene?
All glass should be collected because more than one type may be present. In addition, if just a few representative samples are saved, individual pieces that could be physically matched with glass remaining in the headlight shell of the suspected vehicle may be overlooked.
Why is glass class evidence?
Very small glass fragments would not fit together well, some fragments would probably not be found at all. This would make it more difficult to put the pieces together and match to the rest of the bottle; so this is class evidence.
How is glass found in a crime scene?
Microscopic fragments of glass can be recovered at the laboratory from items of clothing, footwear or hair combings of a suspect. Such fragments can also be recovered from implements e.g. baseball bat that may have been involved.
Why is it important to collect all the glass from a scene?
All glass should be collected because more than one type may be present. In addition, if just a few representative samples are saved, individual pieces that could be physically matched with glass remaining in the headlight shell of the suspected vehicle may be overlooked.
Why is glass class evidence?
Very small glass fragments would not fit together well, some fragments would probably not be found at all. This would make it more difficult to put the pieces together and match to the rest of the bottle; so this is class evidence.
What are the two most often used methods of glass analysis?
The projects focus on the two elemental analysis techniques X-Ray Fluorescence (XRF) and Laser Ablation Inductively Coupled Mass Spectrometry (LA-ICP-MS) that are commonly used by forensic glass analysts.
What is the role of glass?
Glass enhances building exteriors and the design of vehicles. Inside it contributes light and space and permits personalisation.
Why is comparative glass analysis important?
There are several reasons for this occurrence. The aim of a comparative glass analysis is to exclude possible sources. When a difference is detected, no further comparison is necessary. Additionally, sampling is typically beyond the control of the forensic scientist and is subject to what happens to be preserved on suspects, on victims, and at crime scenes. The glass must then be recovered.
Why is it not possible to assess every potential point of comparison in each glass specimen?
It is not always possible to assess every potential point of comparison in each glass specimen because not all fragments transferred, recovered, and submitted for forensic analysis will express every feature. If a fragment does not possess a particular feature, it is not necessary to assess that feature in comparison specimens. For example, not all glass fragments will possess original surfaces. Without original surfaces, it is impossible to determine the thickness of the glass. It would therefore be pointless to measure thickness in one glass fragment if the fragment it was being compared with does not possess original surfaces.
How far can glass fragments be ejected?
During experimental studies, glass fragments have been recovered from up to four meters away from a breaking glass object (Francis 1993; Locke and Unikowski 1991). Glass fragments can be transferred onto anything within this distance. The number of glass fragments that can be transferred is controlled by a number of factors:
How many fragments of glass are generated by a break?
The number of glass fragments generated by a break is independent of the size and thickness of the window but increases with greater damage to the glass (Locke and Unikowski 1992).
What is laminated glass?
Laminated glass is produced by heat-sealing thin layers of plastic between two or more panes of heat-strengthened glass. In the United States, laminated glass must be installed in the windshields of vehicles, and tempered glass must be installed in the side and rear windows (U.S. Department of Transportation, Code of Federal Regulations [CFR], 49 CFR 571.205).
What is the raw material used in glass making?
The vast majority of the raw materials used for making glass are derived geologically. North American glass manufacturers annually use more than 20 million tons of raw materials (Carr 1994). In addition to the geologically derived raw materials, recycled broken glass, or cullet, is added to the batch to act as a flux, and some manufacturers use synthetic soda ash (Na2CO3) (Guttman 1996). All of these materials contain impurities that can produce measurable variations in the final glass product.
Why do forensic laboratories not use SEM-WDS?
Most forensic laboratories do not use SEM-WDS because of its higher cost and greater complexity (SWGMAT 2005a). Although SEM-WDS is available in the FBI Laboratory, it is not used for glass analysis because of the availability of more discriminating chemical analysis techniques. Therefore, it will not be discussed in this paper.
