Trace evidence is microscopic evidence at the scene of a crime and occurs during a criminal act. Trace evidence occurs when the criminal makes contact with an item in his or her surroundings. When this contact occurs, the perpetrator may pick up or leave traces of evidence. The transfer of evidence is the Locard exchange principle. The Locard exchange principle or Locard’s theory was the belief held by Dr. Edmond Locard, a French forensic scientist who according to the Journal of Behavioral Profiling, “states that with contact between two items, there will be an exchange”.
Types of Trace Evidence
Dr. Edmund Locard established the first crime laboratory, in Lyon, France also and founded many of the forensic techniques used in the forensic field today. Microscopic trace evidence traditionally exhibits in the form of bloodstains, fingerprints, hair, cosmetics, plant, mineral or synthetic fibers, glass, paint chips, soil or other botanical materials, residue from gunshots, explosives, or volatile hydrocarbons, and is difficult to identify with the naked eye. Although difficult to discern visually, trace evidence often provides the missing link in solving a criminal case. Additionally, it may be the key that links multiple crime scenes when a serial crime occurs.
Preventing Trace Evidence Contamination
The most important aspect involved in trace evidence is to preserving the integrity of a crime scene. Once a crime is determined to have occurred, securing the perimeter is essential in preventing the contamination of forensic evidence. Whenever someone enters or leaves the scene of the crime, it increases the risk of contaminating the forensic evidence and can compromise the investigation. Only essential forensic investigators should enter until all evidence is collected.
The National Institute of Justice defines trace evidence as a way “investigators can potentially link a suspect and a victim to a mutual location through trace evidence. For example, a fiber sample obtained from a suspect's person can be identified through scientific analysis as originating from a garment worn by the victim. The analysis of the fiber evidence can help establish if the victim and suspect were in the same area.”
Evidence Chain of Custody
Determining whether something is criminal evidence versus being part of the immediate environment can be difficult initially. If in doubt, it is always beneficial to collect what may be trace evidence as one only gets one chance to collect the evidence. Later further examination may eliminate its value to the investigation but better to eliminate than hesitate.
Trace evidence can make or break a case or connect multiple cases in serial crimes. There is a legal chain of custody that dictates how trace evidence is collected and breaking the steps of the custody chain cause the evidence to be inadmissible in court. When collecting forensic evidence it is imperative standard protocols be followed to preserve the evidence legally for future legal proceedings.
Resources:
Journal of Behavioral Profiling “Evidence Dynamics: Locard's Exchange Principle & Crime Reconstruction” (accessed October 25, 2011).
National Institute of Justice “Trace Evidence” (accessed October 25, 2011).
Erika Lyn Smith - Erika Lyn Smith - is a Psych RN, who has completed the UMSL Medicolegal Death Investigator Training Course, and is finishing a BS in ...
