The primary principle which serves as the basis of crime scene investigation is undoubtedly the Locard’s Exchange Principle. According to the principle, whenever a person or rather a living subject enters or leaves any particular environment, something of physical form is either added or taken away from the scene. The principle is summarized by the statement “Every contact leaves a trace.” (Crime Scene Investigation, n.d) This principle enables crime investigators to link suspected persons to scenes of crime, victims, and to physical objects.
Objects or materials in any form that could be relevant in crime are referred to as physical evidence. However, not all types of materials qualify as evidence but only objects or materials that could provide significant probative clues related to a crime such as associative evidence. Associative evidence refers to any physical evidence that links a suspect to the scene of a crime. According to Girard (2017) associative evidence serves two functions: it can either associate a person to a particular crime or rule them out as persons of interest in the crime. Although the main intention of associative evidence is to implicate suspects, it does the opposite; it mostly exonerates individuals from a suspicion that implicates them. Examples of associative evidence include “blood and other body fluids, fingerprints, hairs, bullets, firearms, and imprint evidence” (Girard, 2017). The aforementioned materials are assumed to be of unknown origin and are only ascertained after making a specialized analysis and comparison to a known sample that is often provided by the suspects, witnesses, or victims.
The two types of associative evidence are identified as evidence with class characteristics and that with individual characteristics. When evidence is analyzed and put under a class, numerous sources remain linked to the crime. On the other hand, when material evidence is individualized, the possible source is only one (Girard, 2017). In summary; associative evidence is used to determine the perpetrators of crime.