Forensic Science is the science which has developed its own Laws and Principles. The Laws and Principles of all the natural sciences are the bases of Forensic Science.
Every object, natural or man-made, has an individuality which is not duplicated in any other object.
1. Law of Individuality
Anything and everything involved in a crime, has an individuality. If the same is established, it connects the crime and the criminal.
This principle at first sight appears to be contrary to common beliefs and observations. The grains of sand or common salt, seeds of plants or twins look exactly alike.
2. Principle of exchange
Contact exchange traces is principle of exchange. It was first enunciated by the French scientist, Edmond Locard. Commonly known as Edmond Locard’s maxim on Interchange.
According to the principle, when a criminal or his instruments of crime come in contact with the victim or the objects surrounding him, they leave traces. Likewise, the criminal or his instruments pick up traces from the same contact.
3. Law of progressive change
“Change is inevitable” , this also applies to object. Different types of objects may take different time spans.
The criminal undergoes progressive changes. If he is not apprehended in time, he becomes unrecognizable.
The scene of occurrence undergoes rapid changes. The weather, the vegetable growth, and the living beings make extensive changes in comparatively short periods.
Samples degrade with time, Bodies decompose, tire tracks & bite marks fade, the firearm barrel loosen, metal objects rust, etc.
4. Principle of comparison
“Only the likes can be compared” is the principle of comparison.
It emphasize the necessity of providing like samples and specimens for comparisons with the questioned items.
A questioned hair can only be compared to another hair sample, same with tool marks, bite marks, tire marks, etc.
A specimen obtained by writing on the same wall, at the same height and with the same instrument and then photographed. It can be matched.
Once handwriting available on a photograph allegedly written on a wall was compared with the specimen written on paper. It did not give worthwhile results.
5. Principle of analysis
The Analysis can be no better than the sample analyzed.
Improper sampling and contamination render the best analysis useless.
The principle emphasizes the necessity of correct sampling and correct packing for effective use of experts.
6. Law of probability
All identification, definite or indefinite, are made, consciously or unconsciously, on the basis of probability.
Probability is mostly misunderstood. If we say that according to probability a particular fingerprint has come from the given source, but it is not a definite opinion.
Probability is a mathematical concept. It determines the chances of occurrence of a particular event in a particular way.
If “P” represents probability, “Ns” the number of ways in which the event can successfully occur (with equal facility) and “Nf” the number of ways in which it can fail ( with equal facility) , the probability of success is given by the formula:
7. Law Of Circumstantial Facts
“facts do not lie, men can and do”
Evidences given by eye witnesses or victims may not always be accurate.
Sometimes victims may intentionally lie or sometimes because of poor senses (such as low sight, unclear hearing), exaggeration & assumptions.
According to Karl Marx “True belief only becomes knowledge when backed by some kind of investigation and evidence”.
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