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Forensics
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The crime scene
Preserving the scene
Types of evidence
Polluting the scene
Recording and preserving evidence
The crime scene
A crime scene is a location at which a crime has taken place and a
location that may yield physical clues as to the nature of the crime
and the person or persons responsible for it.
Securing The Scene
Once a police officer has determined the area to be regarded as a
crime scene he or she must make it inaccessible to all but
authorised personnel such as other police officers, Scenes of Crime
Officers (SOCO) and a police doctor - or pathologist. It is important
that the integrity of a crime scene is maintained wherever possible
so as not to contaminate any evidence that may be available.
Protecting Evidence
If the crime scene is located outside then the officer may find it
necessary to place a cloth or waterproof sheeting over anything that
he or she might consider to be evidence. It is also important to note
at this point that anything can be evidence - from the largest item
to the smallest thing such as a cigarette end or piece of tissue.
Anything that might look out of place in its current location more
often than not is out of place and should be considered to be
evidence.
Protecting The Scene
It is of the utmost importance that members of the public and press
are kept at arms length not only to preserve the crime scene but
also to keep details of the crime to a minimum; too much
information in the public domain can influence the outcome of any
police investigation and can also lead to unwanted hoax calls and
false confessions.
It is important to mark out footprints and tyre tracks that may have
been left by the perpetrator of a crime and doing this can be done
with tape or paper if it is available.
The police may also erect tents or tarpaulins to minimise the view of
a crime scene to both press and public and also so that a police
doctor or pathologist can carry out a cursory examination of a
corpse before it is moved for autopsy.
An officer who is first on the scene is also required to segregate any
witnesses to the crime - if there are any - and make sure they are
kept away from the media. Officers are also encouraged to make
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notes of strange smells or fragrances that may not be present at
the time when the Scene of Crime Officer arrives.
All of these things are important and can provide vital information
for Scene of Crimes Officers when they arrive on the scene. Crime
scenes are often the most valuable resource when it comes to
evidence and as such should be treated with care and due attention
so that any vital clues are preserved and uncontaminated.
Polluting the Scene
When referring to the chemical pollution of a crime scene we refer
to any substance that may make the identification of DNA, fibres,
fingerprints or other forensic material difficult. Such chemicals are
often found in nature and indeed often contaminate a crime scene if
the crime scene is outdoors. Sources of chemical pollution in
outdoor crime scenes can include:
 Rainwater
 Seawater or water from a river
 Oil, petrol or diesels
 Soil
 Chemicals used industrially
All of the aforementioned contaminates are found either in nature or
as a result of human intervention. They can be found in and around
a crime scene either because they were already present at the
crime scene or because they have been transported unwittingly to
the crime scene.
Preventing Chemical Contamination of a Crime Scene
In some cases it is impossible to prevent the contamination of a
crime scene especially if there has been rain prior to the discovery
of the crime scene or if the crime scene is in or around a river or
large body of water.
Rain is a highly effective vehicle for the transportation of
contaminates as chemicals from other areas rise into the
atmosphere and are then deposited elsewhere during rainfall.
Chemicals that make their way into bodies of water are also easily
transported as they will travel in the direction the river, lake or
subsequent water track follows.
How Do Humans Prevent the Contamination of a Crime
Scene?
Wearing protective clothing whilst examining a crime scene.ensures
that the technicians (a) do not bring any foreign debris or chemicals
to the crime scene and (b) do not remove anything from the crime
scene.
Technicians are also required to wear protective footwear such as
paper slippers which prevent them from carrying anything to or
from the crime scene on the soles of their shoes. It is also
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important to remember that at the scene of a crime the first police
officer – or officers – has the responsibility of cordoning off the area
to ensure that no one enters or leaves. This is designed to ensure
that no cross contamination occurs.
On occasion the officers who are first on scene will be required to
provide their fingerprints to rule out any fingerprint evidence that
may have been contaminated by their touch.
Recording and Preserving
Once a crime scene has been established it is important that all
evidence is collated, catalogued and recorded for further reference.
This task is normally performed by the Scenes of Crime Officer
(SOCO) and is carried out using a variety of methods.
Methods of Preserving and Recording
Evidence that is loose and perhaps lying on the ground should be
bagged up and catalogued; each piece of evidence is given an
individual identification number so that it can be cross-matched
against corresponding investigative reports. The evidence is bagged
in clear plastic bags, which are sealed airtight so that no
contamination can take place.
Each of these bags is accompanied by a 'custody chain' document;
this document is to be filled out by any officer who wishes to use or
view the evidence. This is necessary to reduce the loss of evidence
and/or cross contamination by individuals who should not have
contact with it.
The area is photographed in meticulous detail and any signs of
injury such as bloodstains are marked, numbered and
photographed. These photographs are often important in the
piecing together of an event so that officers who were not able to
attend the scene can get an understanding for how it looked.
Nowadays with the advent of technology digital technology such as
video cameras are also used to record the nature of the scene.
SOCO may also make audio recordings as to their findings while
they go.
Fingerprints are taken where possible and if the crime scene is
outdoors the area is marked out and searched; these searches can
take the form of a linear search (a single row of officers moving in
unison in a straight line), a grid search (a single row of officers
moving in unison in a series of squares), a quadrant search (one
officer is allocated a particular area of ground to search) or a spiral
search (officers start from the middle of the crime scene and work
their way outwards in a spiral pattern so as to identify possible
pieces of evidence that have spread further than the crime scene
itself.
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Soil samples are also taken as the chemical make up of soil will vary
from place to place; a corpse may have soil on the soles of their
feet or under their fingernails, which may not have been gathered
at the location where the body was found.
It is sometimes necessary for dogs to be used at a crime scene; this
is done so that evidence that may not be visible to the naked eye
can be detected.
Internal crime scenes are photographed, blood spatter patterns are
measured and documented, and bloodstains on carpets and floors
are measured for radius.
Regardless of the location of a crime scene it is imperative that all
of those personnel involved in the recording and preserving of it are
dressed correctly in protective clothing. This clothing which normally
takes the form of plastic trousers and jacket; protective hat (to
minimise the possibility of the hair of those personnel investigating;
contaminating a scene), and shoe covers which are used to reduce
the risk of bringing materials from other locations to the scene of
the crime.
Trace Evidence
Trace evidence is best described as any small piece of evidence that
has to be collected by Scenes of Crime Officers (SOCO) and places a
suspect at the scene of a crime.
What is Trace Evidence?
Trace evidence normally takes on the form of one of the following:
 Hair
 Fibres
 Grass
 Glass
 Soil
 Blood Flecks
 Skin
The Importance of Hair and Fibre
Hair and fibre are two of the most important resources in Forensic
Science and are often responsible for providing valuable clues as to
the identity of an assailant or attacker.
The discovery of hair on the body of a victim or on the clothes of
someone who has been the victim of an assault can often be used
to determine race and sex. It can also be used to extrapolate DNA
for comparison.
Although hair is classified as benign dead matter it still contains
DNA even though the hair itself is not actually a living organism but
is merely pushed through the follicles of the scalp, arms, legs or any
other part of the anatomy where hair is found.
Fibres too are an important discovery and can go some way to
determining what an attacker or killer was wearing at the time of
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the incident. Many forensic scientists use fibres as a means of
determining the nature of the item worn and in some instances can
be as precise as to identify the make of the garment and thus the
manufacturer. In some instances this technique is so successful that
garments that are rare or indeed specially made can be identified
and thus a list of possible suspects drawn up simply by the number
of units sold.
Using a microscope
1.Always carry your microscope with both hands. Grasp the arm
with one hand and place the other hand under the base for support.
2. Turn the revolving nosepiece so that the lowest power objective
lens is "clicked" into position (This is also the shortest objective
lens).
3. Your microscope slide should be prepared with a coverslip or
cover glass over the specimen. This will help protect the objective
lenses if they touch the slide. Place the microscope slide on the
stage and fasten it with the stage clips. You can push down on the
back end of the stage clip to open it.
4. Look at the objective lens and the stage from the side and turn
the coarse focus knob so that the objective lens moves downward
(or the stage, if it moves, goes upward). Move it as far as it will go
without touching the slide!
5. Now, look through the eyepiece and adjust the illuminator (or
mirror) and diaphragm (Figure 3) for the greatest amount of light.
6. Slowly turn the coarse adjustment so that the objective lens goes
up (away from the slide). Continue until the image comes into
focus. Use the fine adjustment, if available, for fine focusing. If you
have a microscope with a moving stage, then turn the coarse knob
so the stage moves downward or away from the objective lens.
7. Move the microscope slide around so that the image is in the
centre of the field of view and readjust the mirror, illuminator or
diaphragm for the clearest image.
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8. Now, you should be able to change to the next objective lenses
with only minimal use of the focusing adjustment. Use the fine
adjustment, if available. If you cannot focus on your specimen,
repeat steps 4 through 7 with the higher power objective lens in
place. Do not allow the objective lens to touch the slide!
9. The proper way to use a monocular microscope is to look through
the eyepiece with one eye and keep the other eye open (this helps
avoid eye strain). If you have to close one eye when looking into
the microscope, it's ok. Remember, everything is upside down and
backwards. When you move the slide to the right, the image goes
to the left!
10. Do not touch the glass part of the lenses with your fingers. Use
only special lens paper to clean the lenses.
11. When finished, raise the tube (or lower the stage), click the low
power lens into position and remove the slide.
12. Always keep your microscope covered when not in use. Dust is
the number 1 enemy!
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base
light source
diaphragm
stage
stage clips
low power objective lens
high power objective lens
8) nosepiece
9) arm
10) fine focus knob
11) body tube
12) coarse focus knob
13) ocular (eyepiece)