This document summarizes the functions of a forensic science laboratory. It discusses how forensic science examines physical evidence for legal purposes, including various specialized fields like forensic pathology and toxicology. It describes how a typical lab provides services like examining victims, conducting chemical analysis, and maintaining a fingerprint and evidence museum. The document also outlines key principles of forensic science like Locard's exchange principle, the importance of control samples, and how physical evidence can be used to connect or disconnect suspects from crimes. It provides examples of different types of evidence and briefly discusses techniques for lie detection and brain mapping that can be used in criminal investigations.

1. FORENSIC SCIENCE LABORATORY
Dr. Santosh Koirala,MD
Forensic Medicine

2. FORENSIC SCIENCE is the study and application of scientific examination and
evaluation of evidence, for legal purpose. It includes,
 Forensic Medicine
a. Forensic Pathology
b. Forensic Psychiatry
 Forensic Toxicology
 Forensic Immunology
 Forensic Odontology
 Forensic Anthropology
 Police science[ voice print examination, polygraph technology,
fingerprinting]

3. Organization/institute
 Clinical services: examination of victims of sexual assault,
sexual crime, drunkenness
 Pathology services: chemical analysis, toxicology, serology,
fingerprints, ballistics
 Museum: fingerprints, bullets and cartridge cases, tyre tread
patterns
 Staffing: medical director, physician, pathologist, fingerprint
experts
 Others: librarian. Liason officer

4. Functions of organization:
 To examine, compare and evaluate physical evidence, so as to link a
suspect o the victim.
 Protection of the innocent, e.g. a person arrested for selling
narcotics, is set free if the chemical analysis of material shows it to
be harmless.
 Training of the police investigators as to be found, collected,
preserved and delivered to the laboratory.

5. Materials:
 Evidence items such as, knives, blunt instruments, blood and seminal
stains, footprints, hair cigars, documents and fragments of various
materials
Criminal investigation: only people commit crimes but they invariably do so
through the medium of objects. It is these objects that together constitute
physical evidence.
Objective of crime investigation:
 To recognize, collect, preserve, analyze, interpret and reconstruction
all the physical evidence collected ( by hands or cello tapes) from the
scene of crime

6. Trace evidence/ physical evidence:
It includes any and all objects, living or dead, solid, liquid or gas,
and the relationship between all objects as they relate to the
problem in question
E.g: crime. A knife, hair, footwear, seeds, pollen, microscopic
fragments of all types, bacteria and even an odor are all physical
evidence.

8. Locard’s Exchange Principle
 When any two objects come into contact, there is always a transfer of
material from each object on the other
 Traces from the scene may be carried away on person, tools of the
criminal or may be left at the scene
 Wherever criminal goes, whatever he touches, and whatever he leaves
will serve as silent evidence against him
 E.g. fingerprints, footprints, hair, fibers from clothes, tool marks,
scratches, blood or seminal stains.

9. Control sample:
 It means specimens of material, e.g. vegetation or soil from the
scene, sample of blood, hair, fingerprint etc. from the victim for
comparison with any questioned material from the crime scene
 Blood stains found on garment, soil, etc. will require unstained
samples to rule out the false positive test due to substrate
interference.

10. LABORATORY FUNCTIONS:
1. RECONSTRUCTION:
the police investigator can reconstruct the events leading up to, during and
sometimes preceding a crime in most cases.
The laboratory helps to make these events more clear.
2. CORPUS DELEICTI:
when a substance is confiscated and the holder is charged with possession of
narcotics, the detection of the substance by laboratory analysis will establish the
body of crime.
3. CONNECTIVE-DISCONNECTIVE MODE:
if certain material found on the suspect are also found at the scene of crime and
vice versa, and of common or similar origin, it will connect the suspect to the
crime, and if there is no similarity, it will aid in disconnecting the suspect from
the crime.

11. Illustarations
The following are some of the illustrations of the usefulness of forensic
science laboratory in criminal investigations.
 Personal identity
 Blood
 Semen
 Firearms
 Fingerprints
 Hair
 Fibers
 Weapons and tools

12. Contd…
 Clothes
 Glass
 Wood
 Metals
 Tool marks
 Paint
 Dust and dirt
 Vegetative material
 Strings and rope
 Tyre marks, documents, photography
 Computer speech labs(csl)

13. LIE DETECTION:
A. POLYGRAPH:
 It is an instrument used to detect lies.
 Keeler polygraph and stoelling deceptograph are in common use.
 Polygraph makes a continuous record of blood pressure, pulse,
respiration, muscular movements and electrodermal reaction changes
in response to stimuli in the form of questions.

14. Contd…polygraph
 It is based on the theory,
 that when the person tells a lie in answer to a question, and there is
fear that lie will be detected, the emotion of fear results in
stimulation of sympathetic nervous system which results in certain
physiological changes( psychosomatic reactions), some of which may
be easily recorded.

15. Contd…
 A question is asked every 20 to 25 seconds, and polygraph chart
recorded in 3 to 4 minutes.
 An experienced and competent polygraph examiner can correctly
detect the truth or lie in about 80 to 90% cases.
 It is also useful in civil cases, e.g. paternity cases, insurance claims,
pre-employment screening by banks and other institutions.

16. B. Narcoanalysis(“ truth serum” drugs)
This is based on the principle, that at a point very close to
unconsciousness, the subject will be mentally incapable of resistance to
questioning, and incapable of inventing the falsehoods that he has used
to conceal his guilt.

17. Contd….Narcoanalysis
 Methods used are:
1. Half mg. of scopolamine hydrobromide, s.c followed by one-forth mg.
Every twenty minutes, for an average of 3 to 6 injections, until the
subject reaches the proper stage for questioning
2. Sodium amytal or sodium pentothal( truth serum) 2.5 to 5% solution i.v.
at a rate not to exceed one ml., until the proper stage is included
3. 0.1 gm sodium Seconal, one and half hours before induction: 45 minutes
later 15mg.morphine sulphate and half mg. scopolamine hydrobromide
are given s.c To save time all three drugs may be given intravenously.

18. Contd…
 Person loses inhibitions and becomes talkative.
 It depress CNS, lowers B.P. and slows heart rate.
 In a state of relaxation, the suspect is susceptible to suggestion and
reveals repressed feelings or memories

19. ….
 The drugs will remove inhibitions, but not self-control
as such, the subject may be able to tell lies, fabricate or
confabulate due to the hallucinatory effect of the
drug.
 This method is risky to the subject. Large number of
false negatives are common.

20. c. HYPNOSIS
Many people cannot be hypnotized/hypnotized to a deep level. It does
not often enhance memory.
Hypnotized witness,
 A. produce more fabricated recollections
 B. are more influenced by interviewer's misleading comments and
questions, and
 C. more confident in the accuracy of their recollections, than are non-
hypnotized witnesses, even when their recollections are false.

21. D. WORD ASSOCIATION:
 Changes in reaction time of the subject’s reply to word stimuli, either
visual or auditory, or by stereotype of answers, or by exhibition of
uncoordinated physical movements, have been employed in attempts
to detect deception.

22. BRAIN MAPPING( Brain Fingerprinting)
 It is a technique that measures recognition of familiar stimuli by
measuring electrical brain wave responses(P300) to words,
phrases, or pictures that are presented on a computer screen.
 It is based on the theory that the suspect's reaction to the details of
an event or activity will reflect if the suspect had prior knowledge of
the event or activity.
 It detects evidence stored in the brain

23. contd…techniques of brain mapping
Modern brain scanning technique consists of:
 Electroencephalography( EEG)
 Magnetoencephalography(MEG)
 Positron emission tomography(PET) magnetic resonance imaging( MRI
and functional MRI) and computed tomography (CT)
 The equipment called ‘ electro-cap’ with 19 electronic sensors is fixed
on the suspect’s shaven scalp for recording EEG

24. ….
 Suspected person is questioned about the crime and also shown the
visuals of the crime scene( victim, weapon, time, place and how he
committed the crime, along with photographs).
 Apart from his verbal replies another computer keeps tract of the
neuro impulses( brain waves, chemical responses) emitted whenever
the visual is seen.
 A specific wave response called MERMER( memory encoding related
multifaceted electroencephalographic response) is elicited when the
brain processes the relevant information it recognizes.

25. ….
 When the details of the crime the perpetrator would know are
presented, a MERMER is emitted by he brain of a perpetrator, but not
by the brain of an innocent suspect. It depends on cognitive brain
responses.
 It is used in crime detection, screening employees, especially in
military and foreign intelligence and counter-terrorism, insurance
fraud, etc.
 It is said to be 100% accurate.

26. THANK YOU!