3. Paradigms and Theoretical Framework of the Research
3.6. Locard’s Exchange Principle
According to Trimpe (2006), the Locard’s Exchange Principle states that “with contact between two items, there will be an exchange” (Trimpe, 2006) or in simpler terms, according to Anonymous on the website forensic medicine (2016a), “every contact leaves a trace” (Anonymous, 2016a).
This basically means that for example, if someone enters a room or a crime scene, they will bring in and leave something behind as well as remove and take with them take something from the room or crime scene which they have been in contact with, along with them, for example, a person who enters a room may drop strands of hair on the carpet as well as pick up fibres from the carpet or beddings while in the room or a perpetrator may leave tyre tracks or shoe prints close to an
54 outdoor crime scene and mud will also be stuck on their tyres or shoes (Trimpe, 2006; Anonymous, 2016a).
The value of trace evidence, also referred to as contact evidence, was first recognised in 1910 by Edmund Locard, hence, this theory has been named after him. Edmund Locard was also the director of the first forensic science laboratory that was established, which was located in Lyon, France. He discovered this principle of exchange after solving a strangulation case by examining fingernail scrapings.
With regards to forensic laboratories assisting with fighting and solving crime in South Africa, Locard’s principle of exchange plays a role in this process. After a crime has been committed, contact with the crime scene must always be kept to a minimum in order to avoid the contamination of the crime scene and possible loss of valuable pieces of evidence that are required by the investigators and forensic laboratories to conduct tests and arrive at a conclusion as to what has occurred at a crime scene and who is responsible for the commission of the crime that is being investigated. For example, if unauthorized personnel enter a crime scene, they will touch things at the crime scene, this will cause them to leave their fingerprints behind on objects that are present at the crime scene such as a light switch, they may also do regular tasks such as drink water or smoke at a crime scene which will result in their DNA being left behind at the crime scene. There are severe consequence to this, such as the wrong person being apprehended and sentenced, especially if collation evidence was not thorough at the crime scene or evidence has been mixed up in the laboratory, due to whichever factors may be prevalent.
Locard’s exchange principle is used as a basis of the collection of physical trace evidence from a crime scene. Trace evidence is small, yet measurable, sometimes almost invisible evidence, such as strands of hair or fragments of the perpetrators skin under the fingernails of a victim, that can be found at a crime scene. Trace evidence is always present in some form or another, no matter how well a crime scene may have been “cleaned up.” Trace evidence may not alone solve a case, however, it may suggest links between other clues or evidence that may have been found at a crime scene, for example, skin under the fingernails of a rape victim may indicate that a struggle had ensued between the victim and the perpetrator and the victim scratched the perpetrator in self- defense. The skin can be tested and analyzed for DNA in order to assist with apprehending the
55 perpetrator of the crime. Examples of trace evidence include strands of hair, partial or complete fingerprints, fibers, glass pieces, paint chips, soil and gunshot residue (Oberg, 2004).
According to Oberg (2004), in most instances, trace evidence, together with the application of Locard’s principle of exchange can be used to attempt to reconstruct a crime scene. There are various examples of the use of Locard’s principle to infer what may have occurred at a crime scene.
Some examples of the application of Locard’s principle are, when paint chips from a hit and run scene are analyzed, they assist in determining the make and model of the perpetrators car. Upon inspection of the car, there may be scratches or missing bits of paint, this will link the suspect to the crime scene. The presence of broken glass at the crime scene of a burglary may infer that a window may have been broken in order to gain entry into the premises. There is a possibility of finding blood on the window pane, even if it has been wiped off, which can be analyzed for the DNA of a suspect. When a firearm is discharged, gunpowder residue is usually left behind, on the hands or clothing of the user of the firearm or on items that may have been close to the location of where the firearm was discharged. In some instances, a suspect may have walked or driven through dirt or stepped in blood at a crime scene, the footprints or tyre tracks left behind would provide information regarding the direction and patterns of movement of the suspect(s). Substances that created the footprints may still be present on the shoes or tyre of the car of the suspect, this will assist to link a suspect to a crime scene.
According to Appel et al (2004), Physical evidence can never be wrong, only its interpretation may contain errors. However, factors that influence the quality and integrity of evidence includes offender actions, victim actions, secondary transfer, witnesses, the weather, decomposition, insect activity, animal predation, fire, fire suppression efforts, the police, emergency medical technicians, crime scene technicians, forensic scientists and coroners, (Appel, 2004; Chisum & Turvey, 2000).
The actions of all parties present at a crime scene, distort the crime scene in some way or another.
This may possibly result in valuable evidence being removed from a crime scene or relocated. This is regarded as the contamination of evidence. Contaminated evidence is evidence that has lost its integrity and is unable to be used to properly and successfully conduct and conclude investigations of crimes that have been committed. If evidence is unlawfully removed or relocated at a crime scene, investigators will not be able to draw meaningful conclusions about the sequence of events that may have occurred at that crime scene.
56 When considering the use of Locard’s exchange principles within forensic laboratories, the laboratories need to be clean and free of any possible causes of contamination. If a laboratory is clean and organised, there is little or no risk of the contamination of any valuable trace evidence, which would result in tests being performed faster and more accurately, as evidence would be easily accessible and not misplaced or damaged due to factors such as negligence. A clean and hygienic laboratory leaves no room for the transfer or loss of valuable evidence and prevents the Locard’s principle of exchange from occurring in a forensic laboratory.
This would also result in cases being closed sooner and the correct perpetrators being arrested and sentenced sooner than the current rate as well as innocent people being freed from incarceration for crimes that they may not have committed. Fewer cases would be struck off the roll and valuable resources would not be wasted and depleted unnecessarily. Just as with the classical school of criminology and the deterrence theory, when cases are investigated and solved sooner, it may possibly serve as a deterrent to possible future offenders as they will rationalise that there is a very high possibility that they will be caught, apprehended and sentenced, or rather punished, which is what human beings seek to avoid and would rather indulge in pleasure over punishment as punishment results in pain and suffering.