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Forensic science
The term forensic science is originated from the Latin word forensis which stands for a forum means belonging to courts of justice. The word term criminalistics is another synonym of forensic science. Forensic science is the most important science which helps in understanding the mystery behind the crime. Forensic science is vast field, its cover different – different field of science and uses its rule and principle for examine the physical evidence and help for handling the clues or identifying the criminals and criminal investigation.

Crime Scene
The place where a crime has been committed or a scene of occurrence of a crime is the place where a particular crime has been committed. The place where an offence has been committed is cannot be limited to one place only, it may extend to one or more place depending upon the nature of crime. The scene of crime can be classified into indoor, outdoor and conveyance crime scene. 	A crime committed on a road or open – air place is an outdoor crime scene. 	A crime committed on house or covered area is an indoor crime scene. 	Conveyance crimes are crimes committed utilizing transportation, such as robbery, carjacking, sexual act, and homicide etc.

A crime scene tells us the real story of criminal act that took place. At that place number of physical evidence has been found by crime science investigators (CSI’s) or forensic scientist. Crime scene can either be primary, secondary and tertiary. For example, in rape and murder investigation, the murder occurred or the person’s life was taken (primary crime scene). And take a woman in another room to rape her that place (secondary crime scene) then transport the women and men to dispose the body (tertiary crime scene).

7 Principles
Forensic science investigation system based on the 7 principle and law’s these principles helps to proper investigation of crime scene and collection procedure and examination of physical evidence which is found from the crime scene. These 7 principles are 1.	Law of Individuality 2.	Principle of Exchange 3.	Law of Progressive change 4.	Principle of Comparison 5.	Principle of Analysis 6.	Principle of Probability 7.	Facts Do Not Lie

Law of Individuality
Every object, natural or man-made, has individuality, which is cannot be duplicated in any other object. It is unique, neither the nature has not duplicated, nor man made. The law of individuality is based on live proof universally true principle. Natural like finger print, foot print DNA, hand writing, sand, seeds of plant and its flower have unique property and man-made things like pen, paper, typewriter, weapons, currency note etc. contain its own unique property that is some time printing block serial number, firing mark, size, shape etc. its look like same but actually its unique in every stage and its duplication is not possible.

Law of Exchange
The French scientist Dr. Edmond Locard first enunciated it, According to Dr. Edmond Locard “when two object come into contact, there is always an exchange of material”. This principle is also known as locard’s principle of Exchange. For Example in the case of rape the accuse may leave semen and that time if struggle has happened between victim and accuse the scratch marks found in accused body and accused skin is found in victim nails also one example is when criminal used any type of instrument to breaks a window or a door, leaves its marks on wooden frame.

Law of Progressive Change
“Everything changes with the passage of time”. Change plays significant role in science as well as in the criminal investigation. In other words nothing is permanent immutable or invariable. The rate of change varies tremendously with different objects.

Principle of Comparison
Different samples can be compared with similar or identical samples. Like bullet samples are compared to other bullet samples, blood samples are compared with other blood samples and likewise so on. Its help to identify the actual weapon and instrument which is used to commit crime, if biological sample has been found, it helps of comparison identify who’s biological samples found in crime and involvement of the person.

Principle of Analysis
To proof involvement of any person and object from crime scene, analysis of the sample is most important part of investigation and chain of custody. In an assault case, the investigating officer collects the clothes of the victim. The clothes carry blood and other biological stains. This sample send to forensic laboratory to analysis, and to find proof the person and object involve in crime scene.

Law of Probability
All identifications, definite or indefinite, are made, consciously or unconsciously, on the basis of probability. Conclusions from forensic analysis are dependent on the method used and its advantage and disadvantage. Probability is a mathematical concept. ‘it determines the chances of occurrence of particular event in a particular way out of a number of ways in which the event can take place or fail to take place with equal facility’.

Facts Do Not Lie
‘Fact do not lie, men can and do’.

Reference

 * 1) https://www.acseduonline.com/courses/science-and-technology-16/introduction-to-forensics-bsc114-820.aspx#:~:text=The%20Law%20of%20Comparison,other%20fibres%2C%20and%20so%20forth
 * 2) https://indianlawportal.co.in/principle-of-progressive-change-and-its-relevancy-in-criminal-invistigation/#:~:text=For%20example%20in%20the%20case,be%20found%20on%20the%20body.
 * 3) https://www.slideshare.net/nhaskar29/principle-of-forensic-science
 * 4) https://askinglot.com/what-is-a-tertiary-crime-scene
 * 5) https://study.com/academy/lesson/crime-scene-definition-components.html
 * 6) https://en.m.wikipedia.org/wiki/crime_scene