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The three major aspects of criminal investigation are (1) to identify the criminal, (2) to locate and apprehend him (3) and to prove his guilt in the court. During the course of investigation an investigator depends on three major tools available to him which are instrumentation, information and, interview and interrogation. Instrumentation helps him to identify or eliminate a suspect by the use of scientific technology thereby analyzing the collected physical evidences whereas the information is transformed into intelligence to identify, locate and apprehend him. But the significance of interview and interrogation cannot be discarded as it plays major role in investigation whenever there is little or no physical evidence.

The difference between interview and interrogation is that an interview is conducted in a cordial atmosphere where a witness is more comfortable physically and psychologically. On the other hand, whenever a person is questioned in an uncomfortable atmosphere (interrogation room) where he is under the psychological pressure, it is an interrogation. Interrogator, in this case, has more psychological advantage than his suspect. Interrogation is a kind of psychological warfare between interrogator and suspect. Only when an interrogator overpowers a suspect psychologically, he gets a confession or the fact of a case which is not possible otherwise.

Interrogation is an art. You can master it through your study and experience. A good investigator is not necessarily a good interrogator. To be a good interrogator you need to be a good actor and must have an insight of human psychology. You should be able to act according to age, profession and intellect of the individual suspect because a suspect could be a lawyer, doctor, scientist, professor, manager or an unskilled laborer and, could be a child, teenager, adult and senior.

Prerequisites of an interrogation:

Before conducting interrogation an interrogator should have the information about:

Suspect:
(i) Name, age, profession, occupation
(ii) Social and financial situation
(iii) Criminal history
(iv) Relation with the victim if any

Victim:
(i) Name, age, profession, occupation
(ii) Social and financial situation
(iii) Criminal history if any

Scene of crime:
(i) Time and place of occurrence
(ii) Modus operandi
(iii) Physical evidence collected
(iv) Information collected

Approach

• Place of Interrogation:
  (i) At the spot when a suspect is apprehended at the scene of crime
  (ii) In an interrogation room where the interrogator has more psychological advantage.
• Time of Interrogation:
  (i) As soon as the suspect is apprehended and information collected
  
• You should always remember that a suspect is innocent and not a criminal unless his guilt is proved in court.
• Don't ever use third degree method.
• Always maintain courtesy.
• Be a good listener.
• Control your anger because in anger you loose reasoning and the judgment made without reasoning is mostly incorrect.
• Never be in hurry to finish the interrogation.

Method of Interrogation

We can classify criminals into two major categories:

• emotional offender

• non-emotional offender

The purpose of classification is to vary your approach and methods during the interrogation of a suspect.

Interrogation of emotional offender:

Interrogation of an emotional offender is much easier than non-emotional offender.

1) An emotional offender is usually a first time offender and can be broken down easily when played with his emotion, ie, love, hatred, anger, frustration etc.

i) By showing sympathy towards him.

ii) By telling him that anybody could do what he has done in the similar situation.

iii) Blaming the society for his action.

iv) Being friendly with him and offering him coke or cigarettes, which an offender never expects from a police officer.

v) Observe his physical reaction to the crime related and non-related questions. When someone is lying he will be under tension. The anti-diuretic bio-chemical substance released by his body leads to the dryness of his mouth and lips. Again in tension he may be tapping his foot, playing with his fingers, looking blankly somewhere else.

2) Emotional offender easily come clean when confronted by the evidence.

Interrogation of non-emotional offender:

Non-emotional offenders are hardened criminals. They are professional who have gained experience committing series of crime and either subsequently have evaded the apprehension or served many jail terms. They don't like to talk much or at all.

• Question and Answer Method: This is a common form of interrogation where an interrogator ask several questions to get the facts of a case. He develops his questions based on the fact of the case and the answers given to him by the suspect.

• Narrative Method: Let the suspect tell his side of story without interruption. Ask him to repeat it three or four times. He will have to tell more and more lies just to cover up one lie. The more he lies, the more you have a chance to detect untruthfulness of his story. Verify his story and re-interrogate him.

• Alibi: Ask where he was and what he was doing at the time of occurrence of the crime. Verify his alibi and re-interrogate him.

• Factual method: The best way to interrogate a hardned and professional criminal is to confront him with the physical and circumstantial evidence, which will eventually lead to his confession.

• Sweet and sour method: Interrogation conducted by two different interrogators, one being soft spoken and other being harsh towards the suspect could be fruitful in some case.

• Overheard conversation method: Whenever there is more than one offender this method works well. One suspect while being interrogated should be viewed but not heard by another suspect from outside of the interrogation room. When his turn of interrogation starts, tell the offender that his associate has already confessed about the crime and now it is his turn to confess.

• Hypothetical situation: Ask a suspect that even he has not done it, how would he have done it in the similar situation. May be some important clue could come out of this.

• Telling the story backward: Sometimes you could ask a suspect his side of story backward. If he has told you what he has done from yesterday 6AM to today 10PM, then let him start from today 10PM to yesterday 6AM

• Bluff Method: Interrogators have used this method for extracting truth from suspects.In this method an interrogator tells a suspect that he has been seen by witness while committing crime or that his fingerprint, footprint or physical evidence have been found at the scene of crime, so there is no choice but to tell the truth. You may be successful extracting the fact in exceptional case but this is not the right method because if the suspect is innocent, the situation is ridiculous.

Interview of Witnesses

There are various kinds of witnesses such as indifference witness, interested witness, hostile witness and child witness. Indifference witness is the best kind of witness for a case because the witness does not have any interest in success or failure of the case. He will always prefer to tell whatever he knows about the case without lying, whereas the interested witness may be a friend, a relative or a potential beneficiary in the case and may exaggerate the fact. As for the hostile witness, he may have close relation or friendship with the suspect and do want to lie to protect the suspect. You may need to interrogate him rather than interview him. Child is a volatile witness who does not lie but is prone to the suggestions.

It is worth to have an eyewitness to support a case but you should also know that his education, technical knowledge, physical condition, profession and emotion influence his observation. Don't expect him to tell everything of what happened when the incident took place. He does not observe as what a police officer needs to observe. His information is valuable if it corroborates to the physical or circumstantial evidence collected. Reconstruction of a case is important to verify the truthfulness of the information of an eyewitness.

Detecting a lie

Polygraph and Computer Voice Stress Analyzer are being used to detect lies. While the Polygraph measures changes in person's body associated with stress of deception- alterations in heart rate, breathing, emoional sweating, the Computerized Voice Stress Analyzer measures changes in voice frequency in the human voice that occur whenever someone is lying. The use of both of these tools are helpful to an investigator to narrow down the area of investigation even though the results are not admissible in the court of law due to the probability of evading a deception.