Polygraphy/ Lie detection in Criminal Investigations

Criminal profiling  -  VIctim, Culprit, Suspect.

• It is done with the help of a sientific instrument called as Truth Verifier. 

• Invented in 1921 by John Augustis,Larsen . They designed the polygraph test used by FBI & CIAA .

• 1st attempt to develop scientific instrument was done by Lambraso (1895). 

• It measures physiological changes such as - BP, Pulse rate, Respiration, Skin conductivity.

• It is also called Deception test. The principle behind polygraph test is Psychosomatic interactions.

• The polygraph test is based on the principe of psychosomatic interactions ( These reactions are result from the stress associated with problem).

• It menifest into physiological changes like BP, Pulse rate, Respiration rate etc.

Instrumentation

Combination of medical devices used to monitor changes.

1. Pneumograph tube - Around the chest, stomach ( For Respirstion ).
2. BP Cuff or Sphygomonometer - On Upper arm 
3. Electrode or Galvanograph - Fix on Index finger and right finger
4. Plathysmograph - On Thumb ( Blood volume reflecting pulse rate ).

Physiological Parameters Measured

The polygraph records multiple signals at once (hence the name poly + graph = “many writings”):

1. Respiration rate (chest/breathing movement).

2. Blood pressure (systolic/diastolic changes).

3. Pulse/heart rate (beats per minute).

4. Galvanic Skin Response (GSR) – sweating alters skin’s electrical conductivity

Testing Procedure of Polygraph Test

1. Pre-Test Phase

• Introduction & Rapport Building – Examiner explains the purpose of the test and assures the subject.

• Consent – The subject must give voluntary consent (very important for legal & ethical reasons).

• Case Discussion – Background of the case and the individual is discussed.

• Question Formulation – Examiner prepares and reviews questions with the subject.

  • Relevant Questions → directly about the crime/event.

  • Control Questions → unrelated but designed to provoke stress (baseline).

  • Neutral/Irrelevant Questions → simple, harmless questions.

2. In-Test (Data Collection) Phase

• Attachment of Instruments – Sensors are attached to record:

  • Pneumographs → chest/abdominal belts to record breathing.

  • Blood Pressure Cuff → measures heart rate & blood pressure.

  • Galvanometer (Skin Electrodes) → records sweating/skin conductance.

• Calibration – Equipment is checked for proper recording.

• Questioning Begins – Examiner asks questions in a structured sequence.

• Recording – Physiological responses are continuously recorded (heart rate, respiration, skin conductance).

3. Post-Test Phase

• Data Analysis – Examiner compares responses to relevant vs control questions.

• Scoring – Stronger reactions to relevant questions → possible deception.

• Discussion with Subject – Sometimes a post-test interview is conducted to clarify findings.

• Report Preparation – Examiner writes a detailed report of results.

Legal aspects of polygraph test in india 

According to Article 20 (3) Fundalmental rights privilege " No person accused of any offence shall be compelled to be a witness against himself" . Thus the result of polygraph test is not accepted in indian courts.

Applications of Polygraph

• Criminal investigations (theft, murder, terrorism).

• Pre-employment screening (esp. in intelligence/security agencies).

• Counterintelligence (detecting spies, insider threats).

• Verifying witness/suspect statements.

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