Pattern evidence is one of the physical evidence that can be found in a crime scene. Forensic scientists are at times accused of neglecting pattern evidence, because they view it as being “non scientific.” This type of evidence has proven to be extremely valuable during reconstruction of crimes and the various activities that might have taken place at the crime scene.
Pattern evidence can be used to prove or disapprove alibis of suspects or the version that witnesses tell about a crime. Pattern evidence is usually created when two surfaces come into contact and impressions, imprints, or markings are formed (Saferstein, 2010).
The impressions formed may be as a result of static or stationary contact or from moving objects. Pattern evidence may also be formed as a result of fractures, breaks, or cuttings by objects (Lee, Palmbach, & Miller, 2001).
One of the pattern evidence that can be found in a crime scene is a glass fracture pattern. This type of a pattern will be found in crime scene that has broken glass. This broken glass can help an investigator to reconstruct the crime scene as well as provide information about the things that happened in the crime scene.
As mentioned earlier glass fracture pattern can be used to approve or disapprove the alibi of suspects as well as determining whether the witness is telling the truth or not. Glass fracture patterns will usually be found in crimes scenes that involve burglary, shootings, and fire. The information that can be drawn from studies carried out on glass fracture pattern includes:
- Direction of impact force applied (from inside out or inside in).
- Approximate force of impact.
- Approximate angle of impact of force.
- Determination of the type of glass fracture.
- Determination of the sequence of firing, direction of firing, and the type of firearm for the projectile holes present.
- Estimation of the fire temperatures, direction of fire travel, and the intensity of heat from the melted glass (Lee, Palmbach, & Miller, 2001, p. 298).
Although glass is known to be hard, it is flexible to an extent. The most flexible glass available is the modern day double pane glass. Glass will break when it is forced to move too much and its breakage will be in a predictable manner. Nevertheless, the amorphous characteristic of glass causes it to scatter fragments that are irregularly sized.
There are various types of fractures that can be made on glass, which include radial and concentric (Girard, 2011). When an object smashes or hits a pane of window it causes the surface of glass to compress and this in turn cause predictable fractures or breaks on it. Primary radial fractures are formed by the first compression impacted on the glass.
These are lines that will originate at the crack formed by the impact and will extend outward corresponding to the force applied on the surface of the glass. The lines will also depend on the shape of the glass. Concentric fractures are also known as secondary fractures and are formed on the same side of the initial impact. They form as the glass tries to counter the tension put by the object on the surface.
This type of fracture will usually show as circles around the hole formed on the surface of the glass. When bullets pass or hit glass panes they usually will leave cone shaped holes that follow the line of trajectory(Girard, 2011).
References
Girard, J. (2011). Criminalistics: Forensic Science, Crime and Terrorism. Sudbury, Mass. : Jones & Bartlett Learning.
Lee, H. C, Palmbach, T. & Miller, M. T. (2001). Henry Lee’s crime scene handbook. Boston : Elsevier Academic Press.
Saferstein, R. (2010). Criminalistics: An Introduction to Forensic Science. Upper Saddle River, NJ : Prentice Hall.