Glass that has been broken or shattered and was discovered at a crime scene is significant forensic evidence. Each common type of glass, including glass from windows, lamps, headlights, and bottles, has distinct characteristics which should be examined differently. Glass that was broken by a hard impact can readily get stuck in a suspect’s shoes, clothes, or hair and can scatter for up to nine feet as same as in the case. If a projectile, such as a gunshot, breaks or shatters a window or other piece of glass, the breakage pattern can be examined to perhaps identify the angle of trajectory of the projectile, providing additional information about the crime, such as the location of the culprit when the pistol was fired. To prevent tampering with the evidence or omitting vital details, it is essential to gather and preserve glass fragment samples from crime scenes properly.
Class characteristics are attributes of physical evidence that can only ever be connected to a collection of sources rather than a single one. Evidence that is found to have class characteristics may be used to narrow the pool of possibilities, but it cannot be tied specifically to one person or source (Saferstein & Roy, 2020). For example, the class evidence can include fibers, paint, and blood type. In this case, the clothing or shores may have blood samples that can be analyzed. Individual characteristics are attributes of physical evidence that are very likely to have a single common source. Examples of the individual evidence can be toolmarks, fingerprints, and anything that contains nuclear DNA (Saferstein & Roy, 2020). Some big glass fragments may have fingerprints of a robber, as such glass fragments need to be examined properly.
The task of the forensic scientist is to continually identify the traits that give matter its distinct identity. Weight, volume, color, boiling point, and melting point are examples of physical characteristics that characterize a substance in isolation from other substances. The major challenge of glass comparison for the forensic scientist is to identify and quantify the characteristics that will link one glass piece to another while limiting or eliminating alternative sources. A forensic scientist assesses two crucial physical characteristics to compare glass fragments: refractive index and density.
A thorough snapshot of the entire situation should be taken before any samples are obtained. The images can be used to show the lengths that the shattered glass has traveled. It is crucial to look for close suspects since any glass fragments left on their bodies (such as those in their shoes, hair, or clothing) are more likely to come off over time and disappear after around 24 hours (Lambert et al., 2022). At hit-and-run accidents, all glass should be recovered. Since headlight glass may be dropped off at a distance when the car leaves the crime scene, the search should not be restricted to the area of collision (Saferstein & Roy, 2020). Glass collected from various areas should be stored in various containers. It is advisable to gather all glass because there can be different kinds there. Individual shards that could be physically matched with glass still present in the headlight shell of the suspected vehicle might also go unnoticed if only a small number of typical samples are kept.
The quantity, size, and distribution of fragments by site provided important information regarding the transfer events. In contrast, the number of glass fragments deposited by primary and secondary transfer varied from a few fragments to thousands of fragments, depending on the closeness and relative location to the breaking glass as well as post-breaking activities, the results show that persistence of glass in people who were not involved with broken glass was low.
When glass is initially broken, the shards are projected from their original site onto everything in the immediate vicinity, be it a person, neighboring furniture, or the scene itself.
The term “primary transfer” is frequently used to describe this initial dissemination (Curran et al., 2020). Evidence can survive even after it has been moved to another area, staying on the original object/person or there. After the initial transfer, pieces, however, rarely remain where they are put since they might be lost through a variety of activities (Curran et al., 2020). On the other hand, secondary transfer may have taken place if glass shards were subsequently displaced to another thing or person.
Collecting and preserving the glass evidence is critical for the case analysis. Glass samples should be gathered from both the typical source (the broken window) and glass shards that are scattered across the floor, furniture, and ground. Each sample must be identified with its source on the label. It is important to gather and name every piece of glass so that, if needed, reconstructions can be built (Lambert et al., 2022). If a suspect is located, samples of their clothing or hair should be gathered for comparison. These could be quite little. When samples are gathered, they should all be dry. Before packaging, damp fragments should be given time to air dry. Use modestly sized containers for little shards to prevent glass from shattering more by bouncing around inside them. Glass samples ought not to be placed in glass vials; instead, cardboard boxes, paper bindles, or other kinds of envelopes ought to be used. These have a lower chance of changing the sample. Any tape used to collect samples should have low stickiness so that it will not stick to itself.
References
Curran, J., Hicks, T., & Trejos, T. (2020). Interpretation of glass evidence. Handbook of Trace Evidence Analysis, 377-420.
Lambert, K., Montero, S., Akmeemana, A., Corzo, R., Gordon, G., Haase, E.,… Almirall, J. (2022). An interlaboratory study to evaluate the forensic analysis and interpretation of glass evidence. Forensic Chemistry, 27, 100378.
Saferstein, R., & Roy, T. (2020). Criminalistics: An introduction to forensic science (13th ed.). Pearson Education.