Pattern Evidence

Pattern evidence is defined as any forensic evidence that can be read and analyzed from a specific type of pattern left by the physical contact between different people (such as victim and assailant), persons and objects (such as victim and automobile), and different objects (such as automobile and tree). These types of pattern evidence can result in various designs such as depositions, imprints, recesses, residues, and striped markings. When injuries result on the victim's body, so-called patterned injuries can oftentimes identify the features of the assailant or object and describe the specific characteristics of injuries. For example, burns result when an assailant shoves a victim into a container of hot water. Burns that are characterized as symmetrical (balanced) and bilateral (appearing on both sides) provide a reasonable initial indication that they were intentional.

Specific examples of sources that often result in pattern evidence include blood splatters (such as from a bullet's exit wound), fire burns (such as from accelerant residue), footwear, furniture positions (such as what results after a fight between victim and assailant), projectile trajectories (such as a bullet's path from an assailant's gun, through a victim, and into an object), shattered glass fractures (such as from vehicle windshields), and tire and skid marks.

Forensic experts examine all forms of pattern evidence in order to eliminate any possible accidental and natural causes for the pattern. For example, fires from flammable liquids often leave behind certain residue patterns. Such fires will normally burn downward unless specifically forced to burn upward. Specifically, accelerants poured from a container will often flow to the lowest spot and accumulate in a pool. After being ignited, the liquid will generally scorch the floor in a puddle configuration. Well-defined boundary lines between the burned and unburned areas will often be obvious to the investigator. In addition, flammable liquids will frequently penetrate cracks and other similar holes, and flow beneath surfaces. The ignited liquid may burn beneath the surface where it was first poured. Areas around such holes will often burn more rapidly when liquid concentrates in those places. All such actions must be considered by the forensic expert.

Pattern evidence, which is for the most part permanent in nature, is often compared to transient evidence, which is evidence that is temporary in nature. Examples of transient evidence that can easily change or disappear include odors, temperatures, and vapors. Forensic scientists, when specializing in pattern evidence, use many different types of instruments and methods to determine the chemical and physical characteristics of pattern evidence. Such professionals also perform investigations of crime scenes to collect and preserve pattern evidence in order to reconstruct relevant events through the analysis of such patterns.