Trace Evidence Essay

Edmond Locard, a French scientist and one of the early pioneers in forensic science believed that “When a person or object comes in contact with another person or object, there exists a possibility that an exchange of materials will take place” (Lynch & Duval, 2011). This theory better known as "Locard's Exchange Principle” is the foundation of the forensic study of trace evidence as we know it today. Trace evidence is very important in forensic investigations as this evidence includes different types of microscopic materials as well as some materials that are easily visible to the naked eye. Trace evidence examination is the analysis of small particles in order to assist in establishing a link between a suspect and the victim of a crime or
At crime scenes where large fragments of glass are available can be useful in linking a suspect with a crime scene through a “mechanical fit”. This is when a larger piece of glass can be physically fitted together with the edge of one or more pieces from the crime scene (Houck & Siegel,). Another example is when a perpetrator or accident victim encounters broken glass they can acquire very tiny pieces of glass on their clothing, shoes or elsewhere. These tiny pieces of glass cannot be physically matched due to their tiny size. However, these pieces though very small and can be identified and characterized under the microscope. After microscopic examinations are performed the Forensic Scientists use microscopic "refractive index" determination to more characteristics of the tiny glass pieces. Refractive index is a measurement of how light is "refracted" (bent) as it passes through the microscopic glass sample. Glasses having different formulations and used for different purposes have different refractive indexes. (Forensic Science Central, 2014) Therefore, the glass removed from from the crime scene could be compared to the source of the glass removed from the suspect's clothes. A great example of this would be identifying a suspected hit and run by matching glass from a possible broken headlight to a victim
Fibers can rarely be used to make an exact positive identification unless torn fibers can be physically matched at their edges, much like the “fractured matches” with glass. Most fiber examination revolves around the possible transference of clothing fibers between people who have come into contact with one another or fiber transfers between a suspect and other environmental elements at the point of contact most notably the crime scene. Fibers can be examined and compared using light wavelengths or microspectrophotometry to determine the color, shade, and shape of the material (Forensic Science Central, 2104). However, individual fibers cannot always be said to come from a particular item of clothing or fabric, but finding fibers with the same common composition on the suspect with fibers from the crime scene can be of great value to an investigation or a prosecution. A great example of this would be completing a fiber analysis to demonstrate that the body of an individual was likely transported in the trunk of an automobile, such as in the Casey Anthony case here in