The document provides an overview of trace evidence in forensic science, emphasizing its importance in linking individuals or objects to crime scenes. It discusses various types of trace evidence, including biological, chemical, and mineralogical, as well as methodologies for blood identification and analysis. Key principles such as Locard's exchange principle and techniques for analyzing materials like glass and paint are also highlighted.

1. DR. SOMASHEKAR C.
ASSISTANT PROFESSOR
Forensic medicine teaching

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What is trace evidence?
• Trace evidence is material found at a crime
scene or accident scene in small but measurable
amounts.
• This is important as it can definitively LINK an
individual or object to the scene.

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What is trace evidence?
Object
Links crime, victim and suspect…
Location
Victim
Suspect

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Importance
“No crime is committed without leaving a clue!!
“Central dogma of any criminalistic investigation
involves recognition, identification, comparison,
individualisation and interpretation of evidence”
“Court / judgement relies on evidence / proof /
witness!”

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Physical evidence
Transient (eg. PM changes, colour of blood stains)
Conditional
TRANSFER/TRACE EVIDENCE
(most diverse and most useful!)
Pattern
associative

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Trace/transfer evidences
Biological (grass, leaves, wood, seeds, pollen etc)
Physiological (blood and other body fluids, hair etc)
Chemical (drugs, poisons, ink, GSR etc)
Mineralogical (soil, minerals, glass, metal etc)
Construction materials (cement, nails, paints etc)
Polymeric (paints, plastics, fibres etc)

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Locard’s exchange principle
.
"EVERY CONTACT LEAVES A TRACE"
The value of trace (or contact)
forensic evidence was first
recognized by Sir Edmond
Locard in 1910. He was the
director of the very first crime
laboratory in existence, located
in Lyon, France.

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Locard’s exchange principle
The Locard’s Exchange Principle states that
"with contact between two items, there will be
an exchange."
For example, burglars will leave traces of their
presence behind and will also take traces with
them. They may leave hairs from their body or
fibers from their clothing behind and they may
take carpet fibers away with them.

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BLOOD/BLOOD STAINS
Blood components
Haemoglobin and derivatives
Blood groups
Haemostasis

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Forensic analysis of suspected
blood stain
Blood stain or not (dry/wet)
Human or animal (species origin)
Haemoptysis/hematemesis/menstrual
Arterial/venous
Tests for blood:

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Presumptive/screening tests
• Negative result means the questioned
stain is not blood
• Positive result means the questioned stain
is likely blood
• exclusary value!

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Presumptive/screening tests
Presumptive tests produce a color reaction or
release of light
Tests rely on catalytic properties of blood
(hemoglobin presence)

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Presumptive /screening tests
RAPID color change is a positive result.
This means the stain is blood.
Color Tests
Apply chromogen (color changing chemical)
Apply oxidizing agent (hydrogen peroxide)
The catalyst of the reaction is hemoglobin

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Color Test Method
• Sample stain with clean cotton swab
• Add drop of chromogen
• Add drop of hydrogen peroxide
Alternatively, collect stain on thread; add
chromogen and hydrogen peroxide in spot plate

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Remember, other non-blood substances
might catalyze the reaction also.
False Positive – A positive result given by
a substance that is not blood
Chemical Oxidants
 Plant materials

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5 Types of Color Tests
• Benzidine
• Phenolphthalein
• O-Tolidine
• Tetramethylbenzidine (TMB)
• Leucomalachite Green (LMG)

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Benzidine
• Positive result = blue color
• Carcinogen (cancer causing) in 1974
• No longer used by sane scientists
Tetramethylbenzidine (TMB)
• Positive result = Blue-green
• Most common test for blood

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Color tests
Phenolphthalein
• Positive result = pink
O-Tolidine
• Positive result = blue
• Similar to benzidine; still carcinogenic as
it can be metabolized to benzidine
Leucomalachite Green (LMG)
• Positive result = Green
• Not as sensitive as TMB or specific as
phenolphthalein

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Presumptive screening tests
• Chemiluminescence and Fluorescence
• Chemiluminescence – light is emitted as a
product of the chemical reaction
• Fluorescence – light is emitted when a substance
is exposed to a shorter wavelength of light
Luminol Fluorescein

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Blood: Confirmatory tests
1.Examination of wet blood
2. Microchemical tests
Teichmann Takayama
(Haemin crystal test) (Haemochromogen test)
3. Haemoglobin derivatives by spectroscopy

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Confirmatory tests
4. Electrophoresis
5. Immuno-electrophoresis
6. Chromatography

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Human blood or not
Species origin:
Most methods test for serum proteins
Serum proteins are found in all animals, but are
slightly different
Species Id methods based on antigen/antibody
interactions

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Species origin
Antibody is in antiserum
Antigen (serum protein) is in blood sample
Human antiserum will only attach to human
blood sample
Antigen = serum protein
Antibody = produced when foreign serum protein is detected
Certain antibody will only attach
to one species’ serum protein

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Species origin
Ring precipitin test
Ouchterlony double diffusion
Crossed over electrophoresis

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Blood stain PATTERN ANALYSIS
Dexter series!!

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Blood stain PATTERN ANALYSIS

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Blood stain PATTERN ANALYSIS

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Determination of blood groups
For Individualising blood/blood stains
1. Blood groups – ABO, Rh, MNS, Kell,
Duffy, Luthern, Kidd etc
Dry blood stain – how to do blood grouping?
A. Latte’s crust method
B. Absorption – elusion technique
C. Absorption – inhibition technique
D. Latex method
Disputed maternity/paternity cases
Crime settings

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For Individualising blood/blood
stains
1. Blood groups – ABO, Rh, MNS, Kell,
Duffy, Luthern, Kidd etc
2. Polymorphisms exhibited by serum proteins
(Hp, Gc, Ag, KM, Gm1, Gm2, etc)
3. Red cell enzymes (PGM, GPT, ADA)
4. HLA typing
5. DNA typing
Application in:
Disputed maternity/paternity cases

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Seminal stains
Settings/scenario: (rape, sodomy,adultery)
Tests:
1. Evidence of spermatozoa (wet mount/stain)
2. Florence test (detects choline)
3. Barberio test (detects spermin)
4. Acid phosphatase test
5. Prostatic specific antigen (PSA)

31. SALIVA
VAGINAL FLUID

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Hairs and fibres
• Hairs and fibers may be transferred from the
suspect or the suspect’s clothes to the victims’
and vice versa. For example, a suspect may pick
up carpet fibers on his shoes or leave hairs
behind at a crime scene.
• Trichology
Hair or not
Animal or human/ body part
Shed/cut/pulled/crushed
Dyed hair
Gender/DNA

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Glass
• Glass particles can be found at various crime
scenes, such as breaking and entering, hit and
run, vandalism, or murder.
• Glass at a crime scene is analyzed to determine
its color, surface characteristics, tint, thickness,
density, chemical composition, and refractive
index (RI).

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Glass
The results of the tests provide clues about the crime
and help investigators connect the evidence to a
suspect or other object used in a crime, such as
matching glass from a crime scene to a headlight of a
suspect’s car.
The pattern of cracks in a windshield
fracture can reveal information about
speed, occupant position, and angle of
impact.
Magnified image of glass fragments

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Paint
• Physical and chemical analysis of paint evidence (chips or
residue) can indicate it’s class, such as automobile paint,
house paint, nail polish, etc.
• The evidence can be compared to 40,000 different types of
paint classified in a database, which can be used to
identify a particular make or model of car or brand of tool

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Paint
• Paint evidence can also indicate individual characteristics
if an investigator is able to find similarities between two
samples, such as the color, number of layers, chemical
composition, or a physical match between the edges of
two paint chips – one from a tool and one from a crime
scene.
Paint Transfer on a
Car
Paint Layers Physical Match of
Paint Chip Edges

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Ballistics
• Characteristics of ammunition, firearms, and
residue are examined to find matches between
suspects and the evidence found at a crime
scene.
• Chemical tests can reveal gunshot residue
(GSR) on the hands, face, or clothing of a
victim or suspect to indicate how close a person
was to a fired gun.
•

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Ballistics
• Rifling (grooves) in a gun barrel causes distinctive
grooves, indentations and scratches upon fired bullets,
which can be matched to the weapon that fired them.
• Police are able to search the Integrated Ballistics
Identification System (IBIS) database to compare
markings from bullets, cartridge cases, and shotgun
shells to ballistic evidence
Investigators can compare
the striations on bullets to
see if they match.

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We learnt…
Trace evidence
Locard’s exchange principle
Blood stain- tests and pattern analysis
Seminal stains
Trichology
Glass/paint/GSR

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Thank You