Trace evidence is based on Locard’s exchange principle which contends that every contact no matter how slight will leave a trace . The trace is normally caused by objects or substances contacting one another, and leaving a small sample on the contact surfaces. Foreign objects or pieces of material present at a crime scene and tracing its origin can assist in an arrest and conviction the same way finding some trace from the victim or crime scene on a suspect can have a strong impact on a case.
Trace evidence, though often insufficient on its own to make a case, may support other evidence or even prompt a confession. Because trace evidence can be any number of things, from a paint chip to a piece of glass to plant debris, there are numerous different methods used for analysis. This essay is to only cover the chemistry unit in the analysis of synthetic material, blood and urine samples, to explore how their work helps in the general aspect of crime investigation and how cases are built using this type of trace evidence.
When it comes to solving cases, evidence is the most important aspect because it links a person to the crime and it becomes their word against science which is used to disprove any alibis’ they may have had or any defenses they may come up with. Not only is what was collected important but how it was collected, what links it has to the crime scene and finally what links it has to the suspect.
The chemistry unit plays a huge part in identifying what the materials collected are as well as analyzing blood samples to match it to someone at the crime scene or any trace’ that may be found at the scene that was left there by someone else or any missing trace’ that could be found somewhere or on someone relating to the crime scene. Trace evidence is used to eliminate suspects and also disprove theories or shape theories as it either strengthens the case or weakens it on grounds of insufficient evidence .
WJ. Chisum, B. Turvey. Evidence Dynamics: Locard’s Exchange Principle & Crime Reconstruction. Journal of Behavioral Profiling; 2000. C. G. G. Aitken, D. Lucy. Evaluation of trace evidence in the form of multivariate data Journal of the Royal Statistical Society: Series C (Applied Statistics) 53 (1), 109122; 2004.