Principles of Forensic Science.pptx HEHEHE

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1. Principles of Forensic Science

2. Principles of Forensic Science Law of Individuality Principle of Exchange Law of Progressive Change Principle of Comparison Principle of Analysis Law of Probability Likelihood Ratio Facts do not lie

3. Law of individuality: Every object, natural or manmade, has an individuality, which is not duplicated in any other object. It is unique. Things might appear indistinguishable to the eye. Egs . Of natural and manmade objects. Principle of Exchange: Whenever two entities come in contact, a mutual exchange of traces takes place. Basic requirement of this principle is the identification of correct sites. Therefore reconstruction of crime scene is important. Egs . Law of Progressive change: Everything changes with the passage of time. Criminals change. Eg. Scene of occurrence. Eg. Objects/weapons/tools change. Eg. Therefore prompt action is essential.

4. Principle of Comparison: Only the likes can be compared. It emphasises the necessity to provide corresponding samples/specimens/standards for comparison. Egs . Principle of Analysis: The analysis can be no better than the sample analysed. Improper sampling and contamination render the efforts of an experienced analyst useless even when he uses correct tools and techniques. Egs . Law of Probability: All identification is done on the basis of probability. Mathematical expression. It determines the chances of occurrence of a particular event in a particular way.

5. Likelihood Ratio: Concept of calculating the chances of occurrence of an event. It takes into consideration the prior factors influencing the occurrence. Chances of occurrence and chances of no-occurrence, both are calculated. Also known as “odds”. Facts do not lie: It highlights the importance of circumstantial evidence vis-à-vis the evidence of eye witness. However, material physical evidence can be manipulated as well.