BTEC Level 3
UNIT 32
Forensic evidence
collection and analysis
Lesson Objective
To be able to gather forensic
evidence from a simulated crime
scene using appropriate methods.
This will include:
• Health and safety
• Evidence collection
• Preservation of scene and sampling
• Analysis and evaluation
What is forensic science?
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the application of a science to answer questions of interest to a
crime.
comes from the Latin forensis, meaning "of or before the
forum."
In Roman times, a criminal charge would be presented before
the public in the forum. Both the person accused and the
accuser would give speeches. The individual with the best
argument would determine the outcome of the case.
Edmond Locard
(1877 – 1966)


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aka “The French Sherlock
Holmes”
formulated the basic
principles of forensic
science
“Every contact leaves a
trace”
Started the first police
laboratory in Lyon in
1910
Scene of Crime Officer

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S.O.C.O.
an officer who gathers
forensic evidence at the
scene of a crime.
usually civilians, not police
officers, but are employed
by the police force.
Evidence collected is
passed to detectives and to
forensic laboratories.
The SOCOs do not
investigate crimes or
analyse evidence
themselves.
Health and Safety


Many jobs require you to
wear personal protective
equipment (PPE).
Activity 32.1A – find a
picture of a SOCO and label
all the PPE they are wearing,
explaining the reason for
using it.
32.1B Risk assessment


What hazards
might be
present here?
What could
you do ensure
risk is
minimised?
Contamination
The unwanted transfer of material which must be avoid
at a crime scene
Individuals can contaminate the scene or evidence at
any time by:
 Leaving fingerprints / hairs / fibres / DNA
 Not sealing the evidence properly
 Putting more than one piece of evidence in a bag at
once
 Using old equipment
Contaminated evidence can not be used in a court of
law and may result in criminals being set free.
HSE Leaflet
Activity 32.1C

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You need to make a Health and Safety leaflet
for a new SOCO to make them aware of
potential risks
You may want to include SOCO PPE and
elements of your risk assessment.
Using the website www.hse.gov.uk, you need
to find 3 piece of legislation to include in your
leaflet.
Processing a Crime Scene
Correct processing of a crime scene is essential to gather as much
information as possible and prevent contamination.
STEP 1
INTERVIEW - The SOCO arrives on the scene and makes sure it
is secure. An initial walk-through is conducted to get a feel
for the crime scene.
The first officer at the scene and/or the victim is interviewed to
ascertain the "theory" of the case; what allegedly happened,
what crime took place, how was the crime committed etc. This
information may not be 100% factual but it will give the SOCO
a place to start from.
The SOCO also needs to find out if anything has been moved.
Potential evidence is noted but at this point, nothing is
touched.
Processing a Crime Scene
STEP 2
DOCUMENTATION – Is the "theory" of the case supported by
what the SOCO observes? Examine the scene to identify
evidence, point of entry and exit, the general layout, etc.
The SOCO thoroughly documents the scene as well as any
potential evidence by taking photographs and drawing
sketches during a second walk-through. Sometimes, a video
walk-through may be conducted. Again, nothing is touched.
Processing a Crime Scene
STEP 3
PROCESSING - Now it's time to touch stuff -- very, very
carefully. The SOCO systematically collects all potential
evidence, tagging it, logging it and packaging it so it remains
intact for further analysis by a crime laboratory.
The lab processes all of the evidence collected at the crime scene.
When the lab results are in, they go to the lead detective on
the case.
Search Patterns
There are several search patterns available for a SOCO
to choose from to assure complete coverage and the
most efficient use of resources.
Search Patterns
1) Inner Spiral
The SOCO starts at the
perimeter of the scene and
works toward the centre.
2) Outer Spiral
The SOCO starts at the
centre of scene (or at the
body) and works outward.
Spiral patterns are good if there is only one SOCO at the scene.
Search Patterns
3) Parallel
The SOCO team form a line
and walk in a straight line, at
the same speed, from one end
of crime scene to the other.
4) Grid
Two parallel searches, offset
by 90 degrees, performed one
after the other.
Search Patterns
5) Zone
The lead SOCO divides the crime scene into
sectors, and each team member takes one
sector. Team members may then switch sectors
and search again to ensure complete coverage.
Activity 32.1D
Search Patterns
You need to investigate the following search patterns:
• Quadrant search (Zone)
• Link Method
• Strip or line search (Parallel)
• Grid
• Spiral Search (inner and outer)
• Wheel or ray method
You will need to include a diagram of the SOCOs pathway through
the crime scene.
Also include any advantages and disadvantages of the search
patterns.
In your opinion, which would be the most ideal search pattern?
What kind of evidence might a
SOCO be searching for?
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Trace evidence (gunshot residue, paint residue, broken glass,
unknown chemicals, drugs)
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Impressions (fingerprints, footprints, tool marks)
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Body fluids (blood, semen, saliva, vomit)
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Hair and fibres
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Weapons and firearms evidence (knives, guns, bullet holes,
cartridge casings)
Documents (diaries, suicide note, phone books; also includes
electronic documents like answering machines, text messages)
Lesson Objectives
• All will be able to:
identify shoe manufacturers’ tread
patterns and wear patterns.
• Most will be able to:
describe the stages of footwear analysis.
• Some will be able to:
explain the theory of footwear analysis to
a jury.
Footprints
Footprints give information
about:
 The number of criminals
 Points of entry and exit
 Position of the suspects
 Direction of movement through
the crime scene.
 Time period (eg short-lived
impressions in frost, snow and
dew)
 Sequence and manner
(walking, running, limping,
staggering).
 The type, size and areas of
wear on the shoes.
Footprints
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Manufacturer, model and size: - general outsole patterns,
shapes, features and markings can help examiners identify the
manufacturer, model and size of the footwear. Can be used to
profile the suspect and provide leads on who may have bought
or worn the footwear.
Approximate height: Investigators refer to statistical data to
approximate the height of the person. Height can also be
approximated by stride length.
Footprints
• Activity of wearer: The footwear imprint left by a person is
different when they are walking, running or carrying something.
An impression left by a running person will be deeper in the
heel and toe sections of the shoeprint. A person carrying a
heavy load will cause deeper prints.
• Link between a print and a piece of footwear: Every piece
of footwear will show different amounts of tread wear and
damage (tiny cuts and nicks).
Footprint impressions
 When
someone walks over
soil, impressions are left in
the ground.
 To
collect the evidence a
frame is built around the
print and suitable casting
material poured in (usually
plaster of Paris) and allowed
to dry.
 The
cast is then removed and
photographed.
How To Cast a Footprint
1.
2.
3.
4.
5.
6.
Place a ruler against the footprint and take a
photograph of the footprint
Frame the footprint with four pieces of card or an
aluminium frame
Apply fixant (hairspray) to help preserve detail.
Mix up the plaster and pour into the footprint
impression.
Leave to harden and then remove cast
When hardened footprint is analysed- nicks, cuts
and worn patterns are noted
Evidence Recovery
Lesson Objectives
All
• To state the different techniques
available for evidence recovery
Most
• To describe each evidence recovery
technique
Some
• Identify the type of evidence that can
be collected via each method.
Labelling evidence
• A description of what the
evidence is: e.g. 103 white
tablets.
• The exact location where it
was found e.g. Oriel High
School, Sc2, corner of teacher’s
desk etc..
• The date and time when
collected.
• The name and signature of the
person that collected it.
Soft Packaging
Grip-seal bags
Tamper evident bags
Brown paper evidence bags
Hard Packaging
Metal air tight tins
Weapons tubes
Cardboard evidence boxes
Activity 32.1F
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You are a SOCO in charge of processing the scene of
a drugs raid. The offender is suspected of producing
and seller illegal drugs.
What types of evidence would you find at this crime
scene?
How would you package each of the items recovered?
How is evidence collected?
Technique
Shaking
Brushing
Taping
Description
Types of evidence
Shake an item over a
large piece of paper and
collect particles that fall
off
Brush surface with a
small brush and collect
debris on paper or in a
container
Trace evidence – glass
fragments, paint chips,
hairs, fibres
Apply sticky tape or gel
lifters to a surface
Removing trapped
particles in shoes,
pockets, hair eg.
Gunpowder residue,
soil, pollen, hairs, fibres
Recovery of fingerprint
or fibres and hair from
dry surfaces
Activity 32.1E
Evidence Collection Techniques
You need to investigate the following techniques
used to gather evidence:
• Casting
• Vacuuming
• Hand picking
• Swabbing
Marks and Impressions
Lesson Objectives
All
• To state the different marks /
impressions that could be recovered from
a crime scene
Most
• To describe how to collect evidence from
different marks / impressions
Some
• To explain what each of the different
marks / impression can tell us
Tyre Prints
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3-D impression left by car wheels in cement,
mud, sand, snow.
Recovered using plaster-casting
Tool marks
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3-D marks left in surfaces eg. Impressions
made in surfaces from breaking in using a
crowbar.
Recovered using putty-casting material.
Teeth marks
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Tooth marks can be left in soft surfaces
(apples, chocolate, skin).
Recovered using putty-casting.
Fingerprint marks
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A fingerprint mark is a deposit of fatty residue
left after sweat has evaporated.
The pattern within the deposit provides a
mirror image of the ridges and troughs of the
finger or palm.
Fingerprint marks
There are 3 categories:
 Latent - the most common type of print, invisible to
the naked eye. Can be seen with powders. Recovered
using taping.
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Visible - resulting from fingers
stained with a substance (ink,
blood, dirt, mud, make-up).
Recovered using taping.
Plastic - this is an impression made by the fingers on
a soft surface (putty, Blu-tack, chocolate). Recovered
using putty-type casting materials.
Lifting fingerprints
1.
2.
3.
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5.
6.
Put gloves on to prevent contamination
Dip the tips of the fingerprinting brush into powder
to pick up a small amount.
Brush gently over the area to be treated taking care
not to smear the print. Continue dusting lightly until
the fingerprint develops.
Cut a piece of lifting tape about 7cm long. Press
firmly over the print. Peel the tape from the surface
in one smooth motion.
Place the tape onto a piece of acetate (lift card).
Place in an evidence bag and label.
Prints are then compared with the national criminal
records database for a match.
Forensic Case Study Activity
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Research a infamous murder case eg The Soham
Murders where Jessica Chapman and Holly Wells were
killed by Ian Huntley.
Identify the types of evidence that the SOCOs would
have looked for at the scene(s).
What were the health and safety issues associated
with the crime scene(s)?