Forensic Science is the scientific discipline engaged in the recognition, identification, individualization, and evaluation of physical evidence by using the laws and principles of natural science to find answers to doubtful questions that may arise in a court of law. These principles of forensic science have a straight impact on criminal proceedings, beginning from the occurrence of a crime until the conviction of the accused in the court of law.
The principles of forensic science which are significant in criminal proceedings are as follows:
Locard’s Principle of Exchange (Law of exchange):
The principle is attributed to a French scientist, Edmond Locard, a criminology and forensic science pioneer, who gave the basic principle of forensic science: “Every contact leaves a trace.” Locard suggested that many traces are left behind, and if appropriately interpreted, they provide the most valuable information.
“Whenever any two objects come into contact with each other, there is always an exchange of minute particles or trace evidence between them.”
According to this principle, trace evidence is left at that site whenever a criminal or his weapon used for the commission of crime comes into contact with the victim or his surroundings/ objects. In the same way, the criminal or his weapons picked up traces from the same contact. Example: In a hit and run case of a road traffic accident, there is a presence of blood stains in the vehicle that has hit and run away. In the same way, the tire marks, footwear marks, and paints of vehicles will be present in the victim’s surroundings. Another classic example is the blood/seminal stain present in the victim of rape, whereas the presence of hair is seen in the accused’s body.
This law forms the basis of scientific crime investigation. This principle is validated in all cases where there is contact, such as fingerprints, tire marks, bullet residues, foot marks, hair samples, skin, muscles, bodily fluids, blood, pieces of clothing, etc. DNA analysis is a straightforward application of this principle, where any such items are under analysis believed to be held by the perpetrator.
Law of individuality:
The principle is attributed to Paul L Kirk (1963) and is regarded as the building block for forensic science. This law implies that every entity, whether person or object, is unique and individualistic. No two things, natural or artificial, can be the same. Even God’s creations, such as seeds, fruits, and plants, are unique. Example: The currency notes, coins, typewritings, etc., are unique, though they look identical or alike.
Kirk claimed that forensic science focuses on the source of two items (questioned and known, or mark and print), which are thought to have come from a single source. As such, identification is concerned with establishing individuality from traces left at a crime scene rather than the sameness of two things. This means identification can be shown indirectly through analyzing traces and samples, e.g., no two fingerprints are identical.
Law of progressive change:
According to law of Progressive change, “Everything changes with the passage of time. In other words, there is nothing permanent and invariable.”
Its impact on criminal investigation is immense. The criminals undergo progressive change as time passes on. If the criminal is not apprehended in time, he becomes unrecognizable except for the fingerprints, blood groups from stains, and DNA profiling. There is also a rapid change occurring at the crime scene. If not secured, the crime scene becomes unrecognizable, and there is a chance of physical evidence being lost, tampered with, or destroyed.
Law of Comparison:
Different samples must only be compared to similar samples. In other words, blood samples are compared to other blood samples, and fibers are compared to other fibers, and so forth.
Law of Comparision states that “only the likes can be compared.” Or “There is a possibility of comparison only when things are similar.”
For example, A bullet from the crime scene can be compared with the firing weapon (rifle) but not with the shotgun; when writing on the wall is to be examined, it has to be compared with similar writing on a wall, not on paper. This is because size and alignments may vary when any individual writes on the paper and the wall.
Law of Analysis:
The law deals with collecting and preserving correct samples for analysis in the prescribed manner to avoid tampering and destruction. That’s because, without a doubt, the quality of any analysis is determined by the quality of the sample under analysis, its chain of custody, and the analyst’s expertise.
This principle states, “The analysis can be no better than the sample analysis” or “The analysis should be done with the proper sampling (correct sampling and packing) is necessary for the right analysis by the experts.”
For example: in the case of seminal stain analysis, the investigation officer collecting the blood-stained clothes will not be of any use. When the explosive material has to be tested, then it should be residual materials collected from the explosion scene, which have the materialistic substance of the blast (there would be no use of testing the soil alone to establish the identity of the explosive.)
Law of probability:
All the identifications and identities are sometimes consciously and unconsciously correct based on circumstances. Also, the conclusions drawn from forensic analysis depend on the method used and its advantages and disadvantages. These must be taken into consideration.
This principle is based on the fact that “all identifications, whether definite or indefinite, are made consciously or unconsciously based on probability.”
Probability is a mathematical concept that determines the chances of occurrence of a particular event in a specific way out of several ways in which the event could take place. Example: In the case of identifying the dead body of a spectacled woman with a nose piercing and a tattoo mark on the right arm.
In conclusion, forensic analysis depends on discovering traces and connecting them to individuals. If no traces are found at a crime scene, it is impossible to identify suspects. However, if traces are found, provided these are appropriately analyzed, and the results are interpreted suitably, they may be used as evidence.
Law of circumstantial facts:
The principle is based on the statement that: “Facts never lie, but men can lie.”
This is concerned with eyewitness testimony, victim statements, and so forth. Anytime people are called upon to provide evidence, there is a chance that the evidence they supply is inaccurate. This can be unintentional (through mistaken observations, making assumptions) or deliberate (lying or exaggerating). On the contrary, evidence that gives a factual account (based on investigation) has a higher chance of being accurate and is more reliable.
Thus, Forensic Science is a scientific discipline directed to the recognition, identification, individualization, and evaluation of physical evidence by applying the principles and methods of natural sciences for the purposes of administration of criminal justice.
