UM - MCJ 2023/24 LQC 7007 18 October 2023

1. THE
PHYSICAL EVIDENCE
PROCESS

2. TRACE EVIDENCE

MCJ 2023/2024
Forensic Science – LQC 7007

18 October 2023
NHJeevan

MCJ-UM 2023/24 1

THE
PHYSICAL EVIDENCE
PROCESS
From Crime Scene
to Court
UM-MCJ 2023/24

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The Five Stages of the

Physical Evidence Process

Presentation

Interpretation

Analysis

Recovery

Occurrence of evidence

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A. Principles Concerning
Occurrence of Evidence

Locard’s Exchange Principle :

“Every contact leaves a trace”

- whenever two objects come into contact
there will always be transfer of material
from one to another and vice-versa

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A. Principles Concerning
Occurrence of Evidence

The degree of transfer of evidence

depends on :

1. The type of evidence

2. The amount of force used
3. The type of surface in contact
4. The duration of contact
5. The type of contact - side swipe, head on,

MCJ-UM 2023/24 5

A. Principles Concerning
A. Principles Occurrence
Concerning
of Evidence
Occurrence of Evidence

Evidence not found/detected does not necessarily

mean that evidence was absent !!
i) Depending on the nature of the objects and the extent of
contact, the amount of material transferred may be very
small, too small to be detected even by today’s
sophisticated methods
ii) Depending on the amount of time that passes, the nature
of the recipient object, and the environment and actions
to which it is subjected, much or all of the transferred
material may be lost prior to the recovery stage

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B. Principles Concerning Evidence

Recovery

First, do no harm -
Nothing should be added, lost, damaged or
obliterated in the recovery process

Avoid contamination –
Care should be taken during recovery process to
avoid contamination

Sufficient evidence sample required

- to enable replicate testing where practical
MCJ-UM 2023/24 7

B. Principles Concerning Evidence

Recovery
Detailed examination of crime scene

Equipment/reagents including test kits used for detection or

screening should be checked for performance before use.

Reference/control samples should be collected

Proper documentation / labelling / chain of custody records

Security and integrity of the item should not be compromised

Safely and securely packaged as soon as possible

- considerations for type of packaging to be used, and for
storage
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Chain of Custody
• To maintain evidence integrity and security

• Is a written chronological record of each person who had

come into possession of the evidence item. Can be a form or
label or tags.

• Custody records to be maintained from the time of collection,

during transfer, storage, analysis, until returned or until
produced in the courtroom.

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Chain of Custody
• Record with case identifier, name and initials of everyone
who handled it, date and time, item description and
location/source of item collected.

• Case identifiers, initials, date etc. and receipts assist in

maintaining chain of custody.

• Best to keep no. of individuals handling the evidence to a

minimum

Any break in the chain of custody will lead to serious

consequences in the administration of justice.

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C. Principles Concerning
Examination/Analysis
• Use of established / validated methods
• Use of appropriate reference standards/materials
(substances).
• Applying quality-control in the analysis
• Non destructive tests to be carried out first before using
destructive analytical techniques;
• Where possible, evidence is not to be used up in the
analysis…… available for re-testing.
• Involves identification and/or comparison of the physical
and chemical properties of the evidence
• Comparison involves using class characteristics and
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individual characteristics of the physical evidence

C. Principles Concerning
Examination/Analysis

Sequence of examination/analysis to be undertaken:

Physical examination – visual; microscopic

Presumptive tests / preliminary tests
Confirmatory tests
Identification/Characterisation
Quantification (if necessary)
Comparison

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Examining/Analysing the Evidence

Forensic examination and analysis

of physical evidence is conducted
for two purposes:
Identification and Comparison

IDENTIFICATION COMPARISON
•To determine the physical or •Subjecting an evidence sample
chemical identity of a and a standard (reference)
substance with as near specimen to the same tests and
absolute certainty as existing examinations for the purpose of
analytical techniques will determining whether or not there
permit. is a common origin.

•What is it? • Does it Match?

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Identification of Physical Evidence

Determination of physical or chemical identity of

substance.
e.g. drug in illicit preparation
hydrocarbon in fire debris
origin of bloodstain – human?
drugs or poisons in blood/urine/organs
explosives
corrosive substance
establishing physical and chemical
properties e.g. of glass, fibres, soil,
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etc.

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Identification of Physical Evidence

Presumptive Tests Confirmatory Tests
Identify class/type Can lead to individual
of evidence classifications
Cheaper Could be costly
Faster Time consumed
Can be done at crime Typically done in the
scene lab
More exact procedure
Less training needed
Could possibly match
Help focus investigation a suspect to a crime
Screening test

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Comparison of Physical Evdience

To ascertain common origin

(possibility/certainty).
Do they come from the same source?
Evidence sample (unknown source) vs.
reference/control specimen (known
source)
e.g. hair, paint chips, soil, glass, bullets
and casings, DNA

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Comparison of Physical Evidence

• Individual
• Class Characteristics
Characteristics
– Properties of
associative evidence – Properties of
that can only be linked associative evidence
with a group and never that can be attributed
with a single source. to a single source with
an extremely high
Examples: degree of certainty or
Soil, glass, paint, probability.
hair Examples:
ABO blood group Fingerprints,
Shotgun pellets DNA profiles,
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Striations on bullets, 19
impression evidence

Class Characteristics
• A single piece of class evidence rarely can be used to
convict someone, but it can be and often is used to
exonerate someone.

• When one is dealing with more than one type of class

evidence, their collective presence may lead to a
higher certainty that they could have originated from
the same source
i.e when multiple types of class evidence associate
one suspect with the crime and crime scene, then
the likelihood of the suspect’s involvement
increases and the case becomes stronger

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Individual Characteristics

Examples:
•The matching ridge characteristics
of two fingerprints

•The comparison of random

striation markings on bullets or tool marks

•The comparison of irregular

and random wear patterns
in tire or footwear impressions

•The comparison of handwriting characteristics

•The fitting together of the irregular edges

of broken objects in the manner
of a jigsaw puzzle

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Analytical Techniques
The spectrum of analytical techniques and
instrumentation used to analyse the wide
range of forensic evidence:
Microscopy (various types)
DNA Analysers
Infra Red (IR) Spectrometry Microscopy
UV-Vis microspectrophotometry
Gas Chromatography (GC)
GC-Mass Spectrometry (GCMS); GCMS-MS
High Performance Liquid Chromatography (HPLC)
Liquid Chromatography Mass Spectrometry (LCMS);
LCMS-MS
Scanning Electron Microscope (SEM)
X-ray fluorescence (XRF)
Etc.etc.etc. MCJ-UM 2023/24 22

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Choice of Analytical Techniques

Should be chosen/applied according to:
• the type of item being examined;
• the quantity of the item to be examined
• the type of question to be answered;
• the sensitivity required;
• the consideration given to quality of results,
processing time and processing cost;
• the availability of suitable instrumentation and
operators;
• the non-destructive or destructive nature of the
technique.

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The forensic scientist should perform a

combination of methods that extract the
greatest potential for discrimination
between samples.
– applies to all types of forensic evidence!!!

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D. Principles Concerning Interpretation

Interpretation gives meaning to the observations/results

of examination
Is used to help answer questions relating to an
investigation or legal proceeding

Principle: Opinions shall be given only based on

information (data/observations/results) obtained during
examination/analysis that is within the area of expertise
and available to the forensic examiner

Relevant questions in a case shall be identified and

possible answers considered

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D. Principles Concerning Interpretation

There are 4 types of questions to be answered:

1. What is the item or evidence (classification, identification)

2. How much is there of the item (quantification)

3. Who or what is the source of the item and could 2 or more

items be attributed to the same source #

4. What happened, when did it happen, who did what

(reconstruction)
(Item 4 may be outside the scope of the lab scientist)
Note: a link between a source and item does not
necessarily provide a link to an activity related to an
offence MCJ-UM 2023/24 26

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D. Principles Concerning Interpretation

Two objects are said to match (be indistinguishable)

when there are no unexplained, forensically significant
differences between them (within the scope of the tests)
An item is said to be individualized when it is matched
to only one source and the forensic scientist is morally
certain that another matching item could not occur by
chance.
Whenever possible, statistical (probability) value or
frequency of occurrence is assigned to physical evidence
e.g. Blood group types
O – 40% , A – 25%, B – 30%,
AB – 5% (= 1 in 20)
DNA profile - 1 in 10 billion (unique??) 27
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E. Principles Concerning Presentation

• A forensic scientist should fully disclose and present

impartial evidence which is readily understandable and
neither overstated nor understated
• Author of report shall not report beyond his area of
expertise
• Reports shall include administrative information,
description of evidence, examination/analysis conducted,
results/findings, & should be traceable to the case notes
• Reports should be peer reviewed and approved before
delivery to customer
• The report and oral evidence should be clear and
unambiguous; shall always present the truth! 28

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What will a forensic report typically contain?

• Admin information on the case: Submitting agency and

officer, date received, report no., lab reference no.,
evidence item markings
• Date of report, name and signature of reporting forensic
scientist/analyst
• Listing and description of all items of evidence examined
received
• Methodology or techniques used in the examination
• Results of the examination
• Interpretation of the data and/or opinion or conclusion.
• Statement regarding disposition of evidence and to include
name of person and date of collection/return. 29

Important Considerations
• Proper Documentation and Detailed Examination of
Crime Scene – understanding of how physical
evidence occurs
• Recognition, Collection, Preservation and Packing
of Evidence
• Chain of Custody – Integrity of evidence
• Security of Evidence
• Correct approach to examination/analysis
• Proper interpretation
• Impartial and Truthful Communication of findings –
report, testimony MCJ-UM 2023/24 30

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THE PHYSICAL EVIDENCE PROCESS

QA/QC MCJ-UM 2023/24

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Physical evidence is the silent witness in

every crime scene, waiting to tell its story
to those who can hear.
It is the voice of justice if recognised,
recovered, analysed, interpreted and
reported/presented properly without bias
and prejudice.
Every stage in the physical evidence
process is a step in the journey to uncover
the truth.

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TRACE EVIDENCE

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What is Trace Evidence?

Trace evidence is small material or evidence
that occurs (during contact) or exists
(thereafter) in very minute quantity and is
used to link victims, suspects, objects, and
crime scenes.

Investigators must carefully document, photograph,

collect and protect the evidence from contamination
before it is submitted to the crime lab for detailed
analysis.
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Examples of Trace Evidence

Biological Physical and Chemical
• DNA – blood, semen, • Paint smears/chips
saliva (automotive and
• Hair – human, animal architectural)
hairs • Explosive residues
• Fingerprints • Glass
• Fibres
Natural • Arson accelerants
• Botanical – pollen, • Acid stains
seeds, plant fragments • Miscellaneous/
• Geological – Soil Unknowns

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What makes a good trace evidence?

Properties/criteria for being an ideal trace
evidence (from a forensic perspective):

(i) has a high probability of transfer and retention;

(ii) is easily visible or observed;
(iii) can quickly be collected and separated,
(iv) can easily be analysed or characterized;
(v) is highly discriminatory

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Recovery/Collection of Trace Evidence

– Techniques Used
1. Hand picking - forceps, magnifier, light
source; applicable to most traces except
stains
e.g. paint flakes, glass fragments

2. Tape lifting - clear adhesive tape to pick up

traces not clearly visible against
background, and also to cover larger areas
e.g fibres on clothings, tiny glass fragments
on clothing

3. Vacuuming – small vacuum pump with

modified suction tube and replaceabe filter
assembly; e.g gunpowder residues from
surfaces/clothings MCJ-UM 2023/24 37

Recovery/Collection of Trace Evidence

– Techniques Used
4. Scraping - scalpel or spatula and
collected in folded paper e.g. paint
smears/flakes

5. Dissolving - solvent action; choice of

solvent depends on the type of trace;
e.g. grease stains, acid stains

6. Swabbing – moistened cotton swab to

absorb biological or chemical stains

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Physical vs. Chemical Properties

• The forensic scientist must constantly determine

those properties that impart distinguishing
characteristics for the purpose of identification or
comparison.
• Physical properties such as weight, volume, density,
thickness, color, boiling point, melting point and
refractive index describe a substance without
reference to any other substance.
• A chemical property describes the behavior of a
substance when it reacts or combines with another
substance. e.g. colour tests for drugs, blood,
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Understanding Analytical Instrumentation

• Analysis of trace evidence requires investigation of physical
and chemical properties
• Because trace evidence is small,…..can’t adequately examine
it with the naked eye
• Caution! Usually sample available for testing is limited.
• Crime labs utilise an array of instrumentation techniques
- Various types of microscopy; ….. Non-destructive
- Spectrophotometry ……………………Destructive
- Microspectrophotometry ………….Non-destructive
- Infrared spectroscopy ………………..Destructive
- Infrared microspectroscopy ……….Non-destrcutive
• Preference for non-destructive testing whenever possible.
(Not possible for biological stains)
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Using the Microscope

▪ Microscope magnifies sample.

▪ Also can look at more detailed

traits of samples.
▪ Many different types of
microscopes are used.
▪ Provides for non-destructive
analysis

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Stereo Binocular Microscope

▪ Look at 3-D objects
▪ Usually look at surface
▪ Preliminary search of objects
(clothes) for small fibers, hairs, etc.
▪ Look at paint chip layers, fibers,
bullet lands and grooves, etc. 5x- 40x

Compound Microscope
▪ Can be binocular or ocular ( one eyepiece)
▪ Look at transparent object on prepared
slide
▪ Examine fibers, hair, glass, sperm cells

50x -200x
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Comparison Microscope
▪ An optical bridge
connecting 2 compound
microscopes allows
viewing of evidence side
by side.

▪ Useful for Comparisons should

comparing be made under the
bullets, fibers, same illumination
hair… conditions at the
same
magnifications.
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Scanning Electron Microscopy

• Used as an imaging and
microanalytical tool in
characterization of trace
evidence such as soil
particles, fibres
• Surface morphology can be
examined with great depth
of field
• Elemental composition can
also be obtained
• Can magnify up to
100,000X
• Uses electrons rather than
light
• Offer much greater
resolution than with a light
microscope
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Micro spectrophotometer
The micro spectrophotometer is sometimes
called a microscope spectrophotometer .
It combines an optical microscope and a
highly sensitive spectrophotometer.
It provides a more objective method of
colour comparison.

Substances absorb, reflect or emit

light in ways that are dependant
upon their chemical structure.

Can be applied to a small spot e.g.

single fibre
Non-destructive Source:
Can discriminate between samples www.microspectra.com

of same colour. MCJ-UM 2023/24 45

Infrared - Micro spectroscopy ( IR

Microscopy)
• IR absorption occurs when the frequency
of the IR radiation matches the
vibrational frequency of a bond in the
molecule and is characteristic of the
chemical composition – provides a
‘fingerprint’ for identification
• Use of microscopes coupled with
infrared (IR) spectrometers has greatly
simplified the IR analysis of trace
evidence such as paint, fibres
• Advantages:
– Non-destructive
– Not limited to sample size
– rapid analysis of micro-samples
– reproducibility of data. MCJ-UM 2023/24 46

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The forensic scientist should perform a

combination of methods that extract the
greatest potential for discrimination
between samples.
– applies to all types of forensic evidence!!!

MCJ-UM 2023/24 47

LOOKING AT SOME TRACES

PAINT
SOIL

GLASS FIBRES

Forensic identification of traces and other substances

require a good understanding of their composition
and both the physical MCJ-UM
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SOIL
• Mixture of organic and inorganic
material
• May range from nearly 100% inorganic
(sand) to nearly 100% organic (peat)
but cannot be entirely of either
• Usually a mixture of sand, silt and clay
• Inorganic part is mineral constituents
– silicates,oxides
• Organic part is decayed plant and
animal material and is sometimes
called humus

e.g. agriculture soil MCJ-UM 2023/24 49

Why soil can be important as evidence ?

• Any crime could possibly leave soil as evidence or a contact

trace:
Rape, murder, kidnap, burglary / theft, hit and run, etc.
Links the criminal, the victim, the scene of crime, the
vehicle, the weapon of offence
Identifies the scene; identifies the place where the
victim/suspect or vehicle came from.
e.g soil on deceased victim different from soil where
body was found, indicating different crime scene
• Many evidence items, bearing soil:
Garden tools – spade/shovels/, wheels, footwear,
clothings, car boot, undercarriage, mudguard gloves, etc.
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Collection and Preservation of Soil Samples

• Should be collected as soon as possible- soil characteristics change over time
• Known or reference samples should be collected at the scene of crime.
• Further control specimens should be collected within a certain radius of the
crime scene; from paths leading into and out of the site
• If the suspect claims to have been elsewhere at the time of the crime, soil
samples from that location should be collected – ‘alibi samples’.
• Since only a small portion is required, sample from top surface is sufficient
• Prior to packaging, the samples should be air-dried.
• All samples collected should be packaged in individual containers. Small
plastic containers are suitable; not paper envelopes or glass containers .
• When a lump of soil is found, it should be packed and preserved intact as e.g
in a hit and run case whereby a lump of soil from undercarriage falls off
upon impact at the scene.
• Soil adhering to shoes, clothing or tools should not be removed. The items
should be air-dried and packaged separately in paper bags.
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Forensic Examination of Soils

Sample Preparation
• Samples are rare rarely ready for comparison when received
• Sample preparation stages include:
drying ;
breaking up of lumps / pulverizing;
sieving; and
‘coning and quartering’.
• Drying of soils are usually carried out in an oven at a
temperature of 1050C – 1100C
• Pulverization is by using a rubberised tool
• Sieving is carried out to remove extraneous material such as
plant fragments, glass fragments, etc.
• Coning and quartering will provide a representative sample and
also allow us to set asideMCJ-UM
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of the sample for additional tests
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Coning and Quartering

https://asdlib.org/imageandvideoexchangeforum/coning-and-
MCJ-UM 2023/24 53
quartering/

Forensic Examination of Soils

Laboratory Analysis
Range of tests depends on quantity of evidence soil
available for comparison
• Colour
Visual and Stereomicroscope
• Texture
• pH
• Particle Size Distribution
• Density gradient
• Mineral analysis
And
• Organic components
• Biological components – Pollen; Bacterial DNA
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Forensic Examination of Soils – contd.

1. Colour
• If 2 air-dried soil samples differ in colour ,
likely that their origin is different;
• To provide uniformity in colour description,
standard colour charts/systems can be used
for comparison and coding the colour.
2. Texture
Texture depends on amount of sand, silt and clay;
If 2 samples of soil have a common origin, then the texture
should be similar.
Texture of air-dried sample is best described after viewing
under a stereomicroscope - fine or coarse, powdery or
granular, gritty or sticky, extraneous material – stones, metals,
glass, seeds, minerals, plant material.
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Forensic Examination of Soils – contd.

3. Particle Size Distribution

4. Density Gradient

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Forensic Significance of Soil

 Soil is generally considered as class evidence – often cannot be
individualized to a particular location
 Soils within a few feet horizontally or vertically differ
 Variability of soil poses problems in sampling
 Significance of a soil comparison is dependent upon the quality of
the sample collection.
 Significance of the finding is enhanced if there is variation
amongst the control samples.
 Sample collection becomes feasible if one can pin point the
location of the incident (e.g.rape/murder case where a shoe print
was also found )
• An unusual soil type may be characteristic of a rather restricted
area and any findings of similarity will be highly significant
What are the limitations??
MCJ-UM 2023/24 57

PAINTS
Paint is any liquid, liquifiable, or resinous
composition which after application to a
substrate in a thin layer is converted to an
opaque solid film.
Paint is used to protect, preserve, decorate
(such as adding color), or add functionality to
an object or surface by covering it with a
pigmented coating.
•An example of protection is to retard
corrosion of metal.
•An example of decoration is to add colour and
lustre to automobile surface or festive trim to a
room's interior;
•An example of added functionality is to modify light
MCJ-UM 2023/24 58
reflection or heat radiation of a surface.

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Importance of Paint Evidence

The importance of paint evidence is to establish :

I. A particular person was at a particular scene.

II. A certain motor vehicle hit a certain individual or another vehicle
or stationary object.
III. A weapon was responsible for inflicting a damage.
IV. A specific tool or instrument was used to effect a forcible entry.

Routine forensic examination of paint evidence involves determination

of :

(a) microscopic features (colur, texture and layering) and

(b) identification of organic and inorganic composition using appropriate
instrument techniques.

MCJ-UM 2023/24 59

PAINT COMPOSITION

Solvents

Binders

Pigments

Fillers/Extenders

+ Additives

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COMPOSITION OF PAINT
Paint consists of four main components
1. Binder holds all the components together and is usually of
polymeric nature, consisting of natural or synthetic resins. Forms
a surface film. Provides adhesion of the paint film to the
substrate; Provides protection properties – resistance to acids /
alkalis / solvents / water etc. and outdoor exposure durability
Different resin types for different applications: e.g. Acrylic
resins – architectural and automative paints; polyester resins –
primers/undercoat; phenolic resins – varnishes; cellulose resins –
lacquers
2. Pigments add colour and hue. They can comprise organic or
inorganic compounds. Pigments are granular or finely powdered
solids
(difference between pigment and dye)
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COMPOSITION OF PAINT
3. Extenders are generally less expensive inorganic materials that
are added to the paint to increase its bulk/solid content and
thereby its opacity and hiding capacity.
e.g. Titanium oxide (also a white pigment), calcium sulphate etc.

4. Solvents which can be either hydrocarbons or water, is used to

dissolve or disperse the binder and assist in the application of
the coating. It is volatile and does not become part of the
paint film …… not much forensic significance.

Additives …. Various chemicals typically added in small amounts

which can greatly affect the properties of coating. Plasticizers (for
flexibility and toughness), Skin forming preventers, UV absorbers
and antioxidants, Drying agents etc.
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Paint Systems
Paint systems are multilayered, because of the following
properties:
adhesion to substrate,
anticorrosion properties,
attainment of the required appearance and
resistance to atmospheric degradation
……… these properties are difficult to attain from a single
layer.
These properties are achieved much more readily by
different paint layers.
MCJ-UM 2023/24 63

AUTOMOBILE SURFACE COATINGS

Usually Consist of Four Paint Coatings
On a modern vehicle the paint vehicle consists of several layers each of which has a
different function.
1. Electrocoat
• First coat onto the steel body by electrodeposition to achieve maximum
coverage because of complex shape of vehicle.
• Uniform in appearance and thickness.
• Provides corrosion resistance.
• The color ranges from grey to black.
2. Primer coat (A primer is a preparatory coating put on materials before the
finishing paint)
• Follows the electrocoat layer and applied before topcoat (colourcoat)
• Ensures better adhesion of paint to the surface,
• Increases paint durability, and provides additional protection for the material
being painted.
• Smoothes out surface imperfections and improve stone-chip performance

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AUTOMOBILE SURFACE COATINGS

Topcoats
Is the finish which gives the surface its required appearance
3. Colour coat:
• Provides the color and aesthetics of the finish.
• Can be divided into 2 major groups – solid colours and polychromatic
colours(metallic)
• Metallic paint has metalllic powder/flakes(e.g. aluminium) in its
formulation

4. Clear Coat:
• No pigments; smooth and transparent
• Improves gloss, durability, and appearance.
• Mostly acrylic-based.
• Protects the base coat
• Originally designed to protect metallic paints,
but is now applied to all colors.

MCJ-UM 2023/24 65

COLLECTION OF PAINT SAMPLES

QUESTIONED or EVIDENCE SAMPLES include all loose or transferred

paint materials.
Sources are: Tools, floors, walls, glass fragments, hair, fingernails,
roadways, transfers on vehicles, clothing items and damaged fabrics
• Should be appropriately packaged and submitted in their entirety.

• Paint on Tool should not be removed. Carefully wrapped at the end

of the tool so as not to dislodge the paint, and the tool is submitted
to the lab.
Smeared Samples: The entire object bearing the questioned paint
should be submitted.
In case of contact between two coated surfaces the samples from
both surfaces should be collected. Possibility of cross transfers should
be considered.
KNOWN or Reference Paint Samples are collected from areas as close
as possible to points of damage or transfer.
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Forensic Examination of PAINT

Physical Features
Color, Layer Structure and Texture are three of the parameters
used.
Color is the most obvious property and in the case of paint smears
it is the only one. The determination and comparison of colour is
the first step to be taken in forensic paint analysis.
Commonly a stereomicroscope is used
to examine the colour, texture and layering of paint
samples
Human Eye is most suited to distinguish among
several colours. But not everyone sees colours in the same way.
Microspectrophotometer also used for colour estimation and is an
objective method for color determination.
MCJ-UM 2023/24 67

Stereomicroscopic Examination of Paint

Obtaining Cross section of Paint fragment
1.The paint is cut straight through it with razor blade and the cut
paint is placed in plasticine or modeling clay. or
2. Embed small brittle pieces of paint in paraffin block and cut the
block with a sharp blade,or with microtome to obtain the cross
section.
The following features are observed under the stereo
microscope (20x - 50x) magnification:
1.The Number of layers of Paint;
2. Color and texture of each layer; (texture – solid
glossy/metallic)
3. Order/Sequence of the layers;
4. Thickness of each layer MCJ-UM 2023/24 68

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OTHER INSTRUMENTATION METHODS FOR EXAMINATION OF PAINT

Microspectrophotometry - for objective

determination and comparison of colour
Infrared Spectroscopy (destructive
technique) or IR Microscopy** (non-
destructive) to identify binders and
pigments for characterisation/composition
of paint samples.
Scanning Electron Microscopy ** – for
elemental composition of paint samples
Pyrolysis Gas Chromatography- Mass
Spectrometry (GCMS) – to analyse
polymeric content of paint …. destructive
** Can analyse individual layers without
having to separate the layers MCJ-UM 2023/24 69

Evidential Value of Automobile Paint depends on

the following factors:

• Type of Paint
• Unusual Pigments
• Probability of another vehicle of the same
color/model at the scene at the same time as the
suspect vehicle
• Layer Structure of paint – thickness and sequence
of layers
• Frequency of occurrence of topcoat colors

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GLASS

Glass is a hard, brittle, amorphous substance

that is composed of silicon oxides mixed with
various metal oxides

MCJ-UM 2023/24 71

Importance of Glass Evidence

• Occurs in variety of crimes
- Hit and run case and other road accident cases
- Burglary cases involving entry thro’ broken glass windows
- Theft of vehicles or theft from vehicles
- Shooting cases involving firing through glass windows/panels
- Assault cases involving broken bottles
• Generally considered as possessing class characteristics. Can be
individualistic due to compositional and manufacturing
differences.
• Evidence not easily destroyed or contaminated, can be collected
and examined at later date.
• Remains unnoticed by culprit when he picks up tiny particles on
his clothings or sole of his shoes or even on his person. Can link
culprit to crime. MCJ-UM 2023/24 72

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Types of Glass
1. Soda-lime glass (commercial glass):
Bottles, jars, everyday drinking glasses, and
window glass.
Not resistant to high temperatures or sudden
change in temperature
2. Lead glass:
Art glass, wine and champagne glass,
etc.
Both soda-lime and Lead glass will not
withstand high temperatures or sudden
changes in temperature.

MCJ-UM 2023/24 73

Types of Glass (contd)

3. Borosilicate glass:
Used in industrial chemical process plants,
laboratories, pharmaceutical industry, bulbs for
high-powered lamps, etc.
Cooking vessels and other heat-resistant
products.
Greater resistance to thermal shock
(compared to soda-lime glass)

4. Laminated glass (Safety Glass):

Holds together when shattered. Has 2
layers of thick commercial glass with a
layer of plastic sandwiched between
them.
Framed glass windows/walls and
windshields

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Types of Glass (contd.)

5. Tempered Glass (Safety glass):
Four to five times stronger than standard glass
Does not break into sharp shards
Shatter into small oval-shaped pebbles when
broken.
Coffee makers, oven windows, computer
screens, skylights, door/windows, shower
enclosures

MCJ-UM 2023/24 75

How Glass Breaks

1. Radial Cracks – Look like lines,
radiating out from the point of
impact.
These cracks form first, and appear
on the opposite side of the glass
(NOT where the force was first
applied)

2. Concentric cracks – Look like

circular rings, each larger than
the other.
These cracks form later and appear
on the same side of the glass (Where
the force was applied.
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Conchoidal Fractures on Edges of Fractured Glass

MCJ-UM 2023/24 77

Which bullet-hole was made first?

radial concentric

MCJ-UM 2023/24 78

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Transfer and Persistence of Glass

Findings from Various studies on primary transfer:

• When a glass breaks, fragments are ejected in all directions

• Backward fragments occur up to 1 m – 4 m depending on the
force and glass type;
• More fragments found on person breaking window than on one
standing nearby
• Size of fragments – usually up to 1 mm
• Every 20 cm., no. of fragments projected backwards - reduced
by half
• More fragments at height of impact
• Can persist on person up to 8 hours
• Movement and other activities will result in loss of fragments

MCJ-UM 2023/24 79

Transfer and Persistence of Glass (contd.)

Findings from Various studies on primary transfer:

• Retention also depends on type of clothing material – less glass on

slick clothing compare to rough clothing;
• Wet clothing retains more glass than dry clothing
• Larger fragments fall off before smaller ones

Primary transfer also can occur when a person or object comes into
contact with previously broken glass.
Additionally, there can be secondary transfer of glass between people
and objects, such as when glass is transferred from a person to a vehicle
seat .
Cannot be positively determined whether the glass fragments found on
an object were acquired through primary transfer, secondary transfer, or
through contact with previously broken glass

Various studies in UK on background level of glass on clothings and

footwear - small percent (0.3 to 3%) of randomly selected individuals
had glass fragments.
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Collection of Glass Evidence

• Must be thorough
• Packaged properly to avoid further breakage
• Suspect’s clothing can be collected to see if it contains glass
fragments – packed in paper
• Fragments can be pieced together to get “the whole picture”
• Or fragment pieces found at a hit-n-run can be matched to the
remaining broken glass of a suspect vehicle

MCJ-UM 2023/24 81

Forensic Examination of Glass Fragments

• For the forensic scientist, the problem of glass comparison is

one that depends on the need to find and measure those
properties that will associate one glass fragment with another
while minimizing or eliminating other sources.
• To compare glass fragments, a forensic scientist evaluates
important physical properties:
Colour
Measurements - thickness, curvature, shape
Density
Refractive index
Elemental composition
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FIBRES
Definition:
The term fibre is used to denote any
solid object that is thin, flexible
and elongate, having a high
length to transverse cross-
section area ratio.
About fibers:
• A fibre is the smallest unit
of a textile material.
• Fibres can occur naturally
as plant and animal fibers,
but they can also be man-
made.
• A fibre can be spun with
other fibres to form a yarn
that can be woven or
knitted to form a fabric.
• Fibres are usually collected
from clothing, carpeting,
furniture, beds, and
blankets.

MCJ-UM 2023/24 83

Importance of Fibre Evidence

Fibres constitute significant evidence of contact between persons or
between an object and an individual. Fibers-specifically, textile
fibres—are common forms of transfer and trace evidence.
Fibres can provide evidence in a large number of instances
▪ Rape and sexual assaults
▪ Weapons and tools may bear fibre fragments
▪ Threads adhering to buttons to a garment
▪ Fibres and cloth fragments from a victim may be found on a hit-
and-run vehicle. Cloth impression on a vehicle surface is an
important evidence in hit and run cases.
▪ Fibres adhering to a bullet provide evidence of the path of the
missile
▪ Shoes may bear fibres from carpet material

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Types of Fibres
• Natural fibres are derived in whole from animal or
plant sources.
- Examples: silk, wool, mohair, cashmere, furs, and
cotton.
• Man-made fibres are manufactured.
- Regenerated fibres are manufactured from natural
raw materials and include rayon, acetate, and
triacetate
- Synthetic fibres are produced solely from synthetic
chemicals and include nylons, polyesters, and
acrylics.

MCJ-UM 2023/24 85

CLASSIFICATION
Fibres

Natural Man-made

Animal Vegetable Mineral Organic Inorganic

[protein] [cellulose] (carbon,
(asbestos)
ceramic,
Hair Silk glass,metal)

Bast Leaf Seed Synthetic Natural

(flax) (sisal) (cotton) polymers polymers

Polyolefin Polyvinyl Poly- Poly- Polyester

(polyethene, (PVC) urethane amide
polypropylene) Regenerated
cellulose
Cellulose Rayon Regenerated Rubber
ester protein
(acetate, (casein)
triacetate)
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Synthetic Fibers
Generic Fiber Type Major Uses

Acetate* Sportswear, lingerie, draperies, uphholstery

Acrylic Sportswear, sweater, socks, blanket

Lyocell* Clothing

Nylon (polyamide) Ski apparel, windbreakers, tents, rope, threads

Garments, ties, dress, lingerie, draperies, sheets,
Polyester
pillow cases
Pantyhose, knitted sportswear, carpets, upholstery,
Polyolefin
furniture

Rayon* Coat linings, ties, bedspreads, lingerie, tablecloths

Spandex (polyurethane) Bathing suits, stretch pants, lingerie

MCJ-UM 2023/24 87
* Regenerated cellulose

Manufacture of Synthetic Fibers

• Melted or dissolved polymer is
forced through fine holes of a
spinnerette
– Similar to a bathroom
showerhead
• Shapes of holes in spinneret
determine cross-sectional shape
of the polymer
• Process is called spinning

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Fibre TRANSFER
• Factors affecting transfer of fibres:
- type of fiber;
- length of fiber;
- type of fabric construction; and
- nature of contact

• The discovery of cross transfers and multiple fibre

transfers between the suspect's clothing and the
victim's clothing dramatically increases the
probability that these two individuals had physical
contact.

• [ When fibres are transferred from the fabric of an

individual's clothing to the clothing of another
individual, it is called a primary transfer. As these
same fibres are transferred to other objects during
subsequent contacts, secondary transfers are
occurring ].
MCJ-UM 2023/24 89

Forensic Examination of Fibre Evidence

The Forensic examination of fibres is primarily carried out in order
to
(i) identify the individual fibre types ( nylon/polyester/cotton etc..);
(ii) determine characteristics that can be used as points of
comparison between the fibres (evidence and suspected/ref.).
Dyed synthetic or natural fibres are more forensically significant
than white cotton or blue denim cotton
• Microscopic comparisons between questioned and standard or
reference fibres are initially undertaken for color and diameter
characteristics, using a stereomicroscope and comparison
microscope.
• Other morphological features that could be important in
comparing fibres are:
- Lengthwise striations on the surface of the fibre
- The presence of delustering particles that reduce shine
- The cross-sectionalMCJ-UM
shape of the fibre
2023/24 90

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Analysis of Fibers
• Step 1: Natural vs synthetic, use microscopy
– Examine the color, diameter, cross-section shape,
pitting or striations, etc.
– Synthetic fibres have smooth surfaces, uniform
size & shape

MCJ-UM 2023/24 91

Microscopy
• Microscopic examination provides the quickest, most
accurate, and least destructive means of determining the
microscopic characteristics and polymer type of textile
fibers.
Acetate Polyester

Cotton Rayon Acrylic

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Analysis of Fibers
• Step 2: Chemical composition of synthetics
• The microspectrophotometer is a convenient
way for analysts to compare the colors of fibres
through spectral patterns.
• Infrared spectrophotometry is a rapid and
reliable method for identifying the generic class of
fibers

MCJ-UM 2023/24 93

Interpretation and Presentation of Findings

Soil, Paint, Glass and Fibres are evidence items that generally have
class characteristics leading to one of these two conclusions:
• Associative conclusion – when questioned sample and reference
sample have matching physical and chemical characteristics
Example: The glass fragments “A1” – “A3” recovered from shirt
“A” demonstrated consistent physical properties (to be specified),
matching each other and the known glass fragments “B”,
indicating that these could have originated from the same source.
• “No Association” conclusion
Example: The glass fragments “A1” – “A3” recovered from the
shirt “A” were consistent in physical properties to each other and
therefore could have originated from the same source. However,
these glass fragments differed significantly in physical properties
to the known glass fragments “B” and therefore could not have
shared a common origin with “B”.MCJ-UM 2023/24 94

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TRACE EVIDENCE - SUMMARY

• Types of Trace Evidence
• Application of the physical evidence process
to some common types:
Soil/Paint/Glass/Fibres
- Occurrence and properties
- Collection of evidence
- Examination & Analysis – techniques used
- Interpretation – significance & limitations
- Presentation of findings

MCJ-UM 2023/24 95

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