Forensic science is that branch of scientific investigation concerned with the basic rules and procedures for analyzing evidence in connection with crimes. These laid principles ensure systematic application of sound practices when forensic experts are asked to uncover the truth.

Types Of Principles

Principle of Individuality

• Natural or artificial, every object is unique and cannot be duplicated.
• Such an identification is helpful with forensic science in corroborating objects.
• Fingerprints, currencies, and machines can all be proved to be highly individualistic.
• In forensic science, this is crucial for differentiating among evidence.
• It assists in identification and solving crime.

Principle of Exchange (Locard's Principle)

• Locard's contribution to crime investigation entails that whenever any two objects come into contact, there is some exchange of materials.
• Each and every person, while entering or leaving a crime scene, takes away certain traces with them.
• Hair, fibers, dust particles, etc., these might also have been exchanged.
• This law can be stated as: Every contact leaves a trace.
• It is of prime importance in the forensic scenario to link suspects to crime.

Law of Progressive Change

• Everything on Earth changes through time because of environmental and external factors.
• Crime scenes and their evidentiary objects also change such that, after a long time, scientific analysis becomes unfeasible.
• This principle clearly emphasizes the need for rapid forensic investigation before evidence degrades.
• Examples include blood becoming dry, fingerprints possibly smeared, and corpse deterioration.
• This prompt collection and possible analysis of evidence.

Principle of Comparison

• Evidence types need to share a common denominator for comparison.
• A blood sample can only be compared with another blood sample and not with anything else.
• Questioned handwriting is compared with known handwriting written with the same pen.
• In the event of an imprinted mark being detected on the wall, the test sample must also be collected from the same height and surface.
• Bringing about fair and valid forensic analysis is guaranteed by this principle.

Principle of Analysis

• Sample analysis hinges on the degree to which accurate the sample collected was.
• Poor sampling and contamination can render the forensic result worthless.
• Proper collection of the specified evidence plus preservation and handling are critical concerns.
• This will guarantee that experts get evidence that is correct and useful for examination.
• This principle outlines the necessity for standardization in forensic work.

Law of Probability

• All identifications and conclusions in forensic science are anchored on probability.
• It describes the chances of an event occurring in a particular manner.
• E.g., calculation of the probability of matching a fingerprint of a suspect to that left at the crime scene.
• Probability establishes facts in forensic conclusions but will not conclusively prove them.

Law of Circumstantial Facts

• "Facts do not lie, men can and do."
• The principle finds emphasis in circumstantial evidence in the conduct of investigations.
• Circumstantial evidence (fingerprints, CCTV camera footage, DNA) is as good as testimonial evidence.
• Physical evidence is not amendable to manipulation or alteration unlike evidence that can be given orally.
• It strengthens the link between the crime and the suspect.