Forensic Polygraphy

2.  Introduction
 History
 Objective
 Equipment
 Requirement
 Preparation of question
 Examination procedure
 Post-test session
 Analysis of polygraph chart
 Interpretation of results
 Limitations
 References

3.  This technique of the detection of deception is based
on the principle of psychosomatic interactions within
an individual.
 For this an instrument named ‘Polygraph’ is used which
can measure and records several physiological
responses such as blood pressure pulse, respiration
(breathing) rhythms, body temperature and skin
conductivity while the subject is asked and answers a
series of questions.

4. This is based on the fact that the fear of
detection and entrapment induces certain
physiological reactions in the body, when an
individual consciously attempts to deceive any
information.
These changes are caused by nervous system.
This polygraph examination can also be known
as psychophysiological detection of deception.

5.  The idea that lying produces physical side effects firstly
started in West Africa.
 Early devices include Cesar Lombroso’s (1885)
invention that measured change in blood pressure and
in 1914 another device was invented which measured
breathing.

6.  The term polygraph was coined by James Mackenzie in
1906. he firstly tried his invention ‘the ink polygraph’
for medical use.
 More advanced polygraph was invented in 1915 by
Harvard trained William Moulton Marston and claimed
that it could detect lies by measuring blood pressure.
 In India tech. was introduced in year 1972-73 at Central
Forensic Science Laboratory (CFSL), CBI New Delhi.

7.  To verify the veracity of the statement of suspect,
witness and complainant in all types of crimes.
 To replace the third degree method of interrogation in
scientific manner.
 To examine white-collar criminals, economic offenders,
and other offenders.
 To economize the process of investigation by screening
large number of suspects by differentiating between the
guilty and the innocent.
 To refute the findings of the investigation.

8.  The equipment which is used for the purpose of lie
detection is the ‘polygraph’.
 The word polygraph means many writings
simultaneously
 As the name indicate the equipment, simultaneously,
can record more then one physiological response and
changes in them
Pneumograph: to record respiration, partially inflated
rubber tube is fastened around thoracic and/or
abdominal region of the examinee

9.  Sphygmomanograph: A blood pressure cuff is fastened around
the right arm
 Galvanograph: electrodes are attached to the index finger and the
ring finger of the left hand for recording the galvanic skin resistance

10.  The examiner
 The examinee
 Polygraph examination room
 Privacy
 Consent of the examinee

11. It involves
 discussion with the investigating officer in detail and
finalizing the issues for conducting the polygraph
examination
 Pre-test interview of the subject with the examiner. It
helps to bring the subject into a proper psychological
set.
 the background information form, and non verbal clue
form, are filled up in order to collect information from
the subject regarding his medical, psychological
,personal history, and crime record.

12. On the basis of the above information three type of
questions are prepared.
 Irrelevant questions: these are not related to the crime
under investigation or any other crime. These are
included because ans. To these questions are admitted
truth
 Control questions: these questions are capable of
provoking emotions, usually about an wrong act which
in general similar to the issue under investigation. These
are less serious in nature and in all probability the
examinee will lie.
 relevant questions: these are directly related to crime
under investigation

13. It involve following steps
 familiarize the examinee with the examination room,
polygraph equipment and its attachments
 instruct the examinee about the manner in which he
has to sit during the examination
 attach the sensors on the examinee
 Record the normal physiological parameters after the
sensors are attached to the examinee.

14.  instruct the examinee regarding the administration of
the questionnaire
 pre test recording is done after the introduction and
review of the questionnaire to the examiner in order to
see the impact of introduction of the questionnaire
 administration of the questionnaire

15.  Get the signature or the thumb impression of the
examinee on the polygraph charts and questionnaires
 Post test interview – this helps the examinee to
understand the meaning and the consequences of the
polygraph examination results.

16.  Steps followed in analyzing the charts are as follows:
 Draw the lines on polygrams at the beginning of each
question i.e. question time and when the examinee
reply the question i.e. reaction time.
 Observe the patterns of normal recordings in all the
four parameters.
 polygraph chart tracing is divided in to four tracing
segments:-
 Average- tracing segments: tracing interpreted as
normal tracing without stress.

17.  Reaction – tracing segment: tracing interpreted as
having observable physiological changes while
answering the relevant questions.
 Relief – tracing segment: tracing interpreted as
having relief reaction after answering relevant questions.
 Distorted – tracing segments: tracing not arising
out of deception but occurs because of other factors.

18.  Observe the normal recordings of physiological
parameters.
 Compare the recordings of each physiological
parameter on each relevant question with respect to
normal recordings, pretest recordings, recordings on
comparison questions and recordings on irrelevant
question.
 Mark the reactions on each and every question on all
the polygrams.
 Sequential analysis is done for each run separately and
the final conclusion is based on the average score of all
the runs.

19. During examination certain precautions have to be taken
by the examiner in order to avoid wrong opinion
formation:
 mental tension of the subject
 unresponsiveness of the subject
 some unobserved muscular movements
 Physiological defects like hearing, impairment,
neurological impairment etc.
 mental abnormalities
These limitations can be eliminated by strictly following
the conditions essential for successful operation of
the polygraph examination.

20.  Sharma .B.R.(1990): Forensic Science in Criminal
Investigation and Trials.
 Klenier.Murry(2000): Handbook of Polygraph testing.
 http://people.howstuffworks.com/lie-detector.htm
 http://www.polygraph.org/
 http://skepdic.com/polygrap.html
 http://truth.boisestate.edu/polygraph/polylaw.html
 http://www.crimelibrary.com/criminal_mind/forensics/p
olygraph/1.html