Fundamental Principles of Forensic Science to be followed and implemented in every step of forensic investigation.

1. PRINCIPLES
OF
FORENSIC SCIENCE
DON CAEIRO
ASSISTANT PROFESSOR

2. 7 Fundamental Principles
Individuality
Exchange
Progressive change
Comparison
Analysis
Probability
Circumstantial Facts

3. Principle of Individuality
 Every object is individual in nature.
 Every object is either man made or natural.
 Certain aspects of an object proves it individuality.
 These aspects are not duplicated in another object.
 Best example - Fingerprints.

4. Principle of Exchange
 Sir Edmund Locard (1910)
 Transfer of material when two objects come in contact with
each other
 Amount of material transferred is directly proportional to the
intensity of contact.
EVERY CONTACT LEAVES A TRACE

5. Principle of Progressive Change
 Changes occur as time passes.
 Has a great impact in the field of forensic science.
 Evidence undergoes changes.
 Crime scene undergoes changes.
 Criminal/suspect undergoes changes.

6. Principle of Comparison
 Likes should be compared
 Samples when compared with standard should be
alike
 For example:
 Signature with signature
 Handwriting with handwriting
 Bullet with bullet
 Cartridge case with cartridge case

7. Principle of Analysis
 The analysis can be no better than the sample analysed
 This means that right sampling is necessary
 This is mainly dependant on the work carried out at the
scene of crime.
 Proper collection, preservation and packaging of
samples and controls is very important to ensure
proper analysis can be done

8. Principle of Probability
 All identifications, definite or indefinite, are made
consciously or unconsciously, on the basis of
probability.
 This brings into the system unbiased approach.
 Statistically proving the probability of events
occurring.
 Through proper experimentation and
statistical calculations evidence is produced and
investigation is done.
Example: Bayesian Theorem

9. Principle of Circumstantial Fact
 “Facts do not lie, men/women can and do”
 Circumstantial evidence is as good as oral
evidence or even better.

10. Thank you