Criminal investigation can be defined in many ways.
It is said to be a series of techniques used in detecting crimes and apprehending suspects. It can also be defined as the act of collecting facts in order to accomplish the aims of criminal investigation. This, of course, includes the use of criminalistics techniques such as lie detection technique or the polygraph.
Another description is that it is the process of reconstructing an incident by deductions based on concrete evidence.
Additionally, criminal investigations can be said to be the legal, truthful, and logical search for individuals and items that can assist in the reconstruction of a crime.
To identify the guilty party
To locate the guilty party
To provide evidence to the suspect's guilt
In relation to that, criminal investigators aim to learn about offenders' tactics, motivations and identities, the identities of their victims as well as those of the witnesses.
These are the fundamental investigatory lines that investigators must pursue in order to get to the truth of a criminal incident:
Who?
What?
When?
Where?
How?
Why?
This is the same 5W's and 1H that have always been used before, except they are being applied towards criminal investigations in this context.
These cardinal points are rooted in these interdependent factors: motivation, opportunity, and means. (Related: Elements of Crime)
These are the basic functions of Criminalistics when it comes to police investigations:
Establishing an element of the crime
Identification of a suspect or victim
Finding associate evidence
Reconstructing a crime
Corroborating collected information
A polygraph examination, also known as lie detection, is a diagnostic test given to someone whose honesty in a statement is in question.
It is carried out by posing a series of questions to the subject while changes in the subject's body is being monitored using a polygraph device.
Polygraph tests are useful for identifying suspects who might attempt to manipulate the judicial system as well as for bringing justice to many innocent people who have been wrongly convicted.
Polygraph tests are useful when there are no reliable and easy ways to differentiate between truthfulness and falsifications.