Criminal Profiling also known as Deception detection tests are part of the investigation when the evidence is not available or doesn’t provide sufficient information about the suspect. These come into the act when forensics fail and police need help in getting a proper direction in the investigation to determine the criminal.

In this article, I will try to help you to understand:

  • What is Criminal Profiling?
  • Deception Detection tests (Lie Detector, Brain Mapping, Narco Analysis)
  • Difference between Criminal profiling and Deception Detection Tests

What is Criminal Profiling? | Role of Criminal Profiler in Crime scene investigation

Criminal profiling or Offender profiling is an investigation of a crime done to understand the nature of crime and personality of a criminal to aid the police in investigating to link the suspect to the crime.

Criminal profiling helps in understanding the patterns, trends of the crime and the way the criminal thinks about a particular crime and victim.

It was limited only to serial killers until the 1990’s when the criminal profiling scope was widened in other crimes as well. It takes years of study, experience and research about psychology to understand criminal profiling.

Who is a Criminal Profiler?

A criminal profiler is an experienced and skilled investigator and psychologist who studies crime, criminal, victim and aids the police in the investigation.

A criminal profiler study about the psychology of the criminals, their behaviour, relationships, background, childhood, parenthood, etc. to understand the motive, personality and reaction to certain circumstances or events.

Criminal Profiling is basically the reverse engineering of a crime scene done by the Criminal profilers in which they understand the victimology (the study of a victim), crime scene and finally the pre and post crime behaviour of the offender to understand them.

To understand the psychology of the criminal many psychologists and criminal profilers go to prison as prisoners to interact with the criminals.

Approach of Criminal Profiler to Crime Scene

For criminal Profiling, the approach of a criminal profiler includes three steps:

  1. How the crime was committed?
  2. Why the crime was committed?
  3. Who committed the crime?

These three steps help the Criminal profiler in understanding the type of offender i.e., Organised or disorganised.

An organised offender would be the one who plans in advance, researches about the victim, weapon planning, etc. while disorganised offender would kill the victim with any weapon without any plan and may leave a bunch of evidence.

Understanding the type of offender would aid the police in identifying the suspects and link them with the crime.

Deception Detection Tests

These tests help in determining whether a person is lying or not. These tests either require a scientific approach or use of drugs which will help in identifying the truth. These tests include:

  1. Lie Detection Tests/Polygraphy
  2. Brain Fingerprinting
  3. Narco Analysis

1. Polygraphy or Lie Detection Tests

A polygraph or Lie Detector test is a machine to reveal the truth from a person. The machine measures certain physiological responses of a person being tested such as changes in Blood pressure, Heart rate, skin conductivity, respiration, anxiety to know whether a person is being truthful or not.

The machine is basically a computer devised software that assesses the response of a person revealing any change in the physiological responses through the graph.

Polygraph or Lie detection test
Source: Unknown

History About Polygraph or Lie Detection Test

First Polygraph was invented in 1921 when John A. Larson devised a system to detect the physiological responses of a person to reveal the truth and aids in deception detection.

Although it was used by Larson in 1921 the credit also goes to William M. Marston who created systolic blood pressure tests and a psychologist Vittorio Benussi who discovered the change in respiration while saying lie.

Compiling the work of all three a complete Polygraph or Lie detector testing machine was invented.

How does Polygraph or Lie detection test work?

A Polygraph instrument is a combination of devices used to monitor changes occurring in the body while answering. it includes:-

  • Pneumograph Tube: The tube is tied around the chest of the subject while another tube around the abdomen to measure changes in the respiratory system.
  • Sphygmomanometer: This instrument is the same as of the physicians and is attached to the upper arm of the subject.
  • Electrodes or Galvanograph: These are like clips which are attached on the index finger and ring finger also on the hand which measure the galvanic skin response by a weak electric current.
  • Plethysmograph: A device attached to the thumb measuring the volume of blood reflecting pulse rate.

Questioning Technique in a Polygraph

The basic approach/steps followed in Polygraph or Lie Detector test while questioning are:

  • Relevant/Irrelevant Question Technique:- Both relevant & irrelevant questions, pertaining to the case in hand are asked.
  • Control Question:- These are interspersed among the relevant & irrelevant questions. They do indirectly relate to the crime under investigation, but to an identical situation during which the answers may have a sense of concern with reference to either its truthfulness or its accuracy.
  • Peak of Tension Question:- It is framed when some of the important details of the offence in question are not made known to the subject. The test questions will have a bearing upon the matter under investigation & all others coming close to the guilty knowledge. the series of questions framed is first read to the subject & later they are administered with the instrument attached.

2. Brain Fingerprinting

Brain fingerprinting was invented in 1995 by Dr. Larry Farwell. It is based on the theory that throughout any action, the brain plans, records, and executes all of the actions. 

“Brain Fingerprinting” is a controversial forensic science technique that determines whether specific information is stored in a subject`s brain by measuring electrical brainwave responses to words, phrases, or pictures that are presented on a computer screen.

Brain Fingerprinting technique
Source: Unknown

Brain Fingerprinting Technique

  • P300 electric signal is emitted from the brain of an individual beginning approximately after 300 milliseconds when it confronts with a special stimulus.
  • It is used in detecting P300 as a response to the stimuli.
  • The machine doesn’t require the subject to respond verbally to any question, rather, the machine automatically detects it.
  • Brain fingerprinting uses responses from the brain and doesn’t depend on the emotions of a subject.
  • In this technique, the subject wears a headband of different electronic sensors which measures EEG from the scalp.
  • The subject watches the stimuli which consist of words or phrases or pictures presented on any computer screen. Those stimuli are of three types:
  1. Irrelevant” stimuli: These are irrelevant to the situation and to the subject.
  2. Target” stimuli: These are relevant to the investigation and known to the subject.
  3. Probe” stimuli: These are relevant to the investigation and subject denies knowing.

Detection of Brainwaves

Three different coloured lines are represented while testing the subject. Those include

  • RED:- This line occurs when the suspect is expected to know the specific information.
  • GREEN:- These brain waves are formed due to the irrelevant stimuli. Information is not relevant to the suspect.
  • BLUE:- This line occurs when the suspect would know about the crime.

Limitations of Brain Fingerprinting Technique

  • Brain fingerprinting reveals information through brain responses. However, it doesn’t reveal the source of the information.
  • Brain fingerprinting is not a lie detection technique, rather, it is a simple information detection technique.

3. Narco Analysis

The term Narco Analysis was coined by Horsley. Narco analysis is a kind of psychological test also known as Truth serum is a scientific investigation method in which a drug is induced in a suspect to obtain information and reveal whether the suspect speaks the truth or not. The suspect goes into a semi-conscious position in which he is forced to speak the truth under the influence of drugs as the suspect loses his/her control over their mind.

Narco analysis is not admissible in courts in many countries including India because of the constitution of India in which Article 20(3) states that “No person accused of any offence shall be compelled to be a witness against himself“.

Therefore, narco analysis of any person requires his/her own consent. If they do not wish to be a part of Narco analysis, constitution is bound to not allow it.

Procedure of Narco Analysis

  • Pre-Test Interview:- Individual is explained regarding the whole procedure and informed consent is taken
  • Pre-Narcotic Test: Anaesthetist induces narco and maintains the pre-narcotic state throughout the interview. The drug is injected till the person appears relaxed and in a state of good contact. The drug given is Sodium pentothal is given intravenously to induce hypnosis. 5% or 10% slowly in the antecubital vein NMT 1gm/grain per minute. As an individual`s speech starts, the interview begins
  • Semi-Narcotic Test: After establishing the semi narcotic state and the individual`s appears to be flushed, slow and slurred speech and Nystagmus.

The individual is allowed to sleep off and allowed to wake up on his/her off. Once she/he wakes up, the anaesthetist checks him/her and allows to drink coffee or tea. The complete narco interview is audio recorded and also written.

  • Post-Test Interview: The memory is checked. The individual is allowed to know what she/he has spoken during the interview. Individuals experience a more relax and anxiety-free state.

Admissibility of Criminal Profiling and Deception Detection Tests in Court

Criminal profiling and Deception detection techniques are not admissible in courts of most of the countries due to the following reasons:

  • The results are not backed by scientific evidence.
  • Criminal profiling is based on the research and observation which can be false as the results may change due to certain circumstances.
  • Deception Detection tests are not reliable as the results may vary in different situations for different persons.
  • There is no such consensus that any evidence through these techniques are 100% reliable. However, they are used to get an idea about the circumstances that might have happened.

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Categories: Psychology


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