Unit 4 - Forensic Investigation Procedures in Practice
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Unit 4: Assignment 4 - Mock Crime Scene: evidence collection
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Unit 4 - Forensic Investigation Procedures in Practice
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A report detailing the collection of evidence from a mock crime scene as well as in-depth descriptions of the methods used at a real crime scene to collect evidence, such as search patterns, common approach paths, crime scene entry logs, and more. Each piece of evidence retrieved from the mock crim...
Unit 4 - Forensic Investigation Procedures in Practice
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Crime Scene Exam
Luke David Farrar
Introduction
A vast variety of different types and forms of evidence at crime scenes require equally
extensive methods of retrieval. Sufficient equipment must be prepared both to preserve the
integrity of the collected evidence, but also to protect yourself from exposure to potentially
harmful substances. To reduce these risks, numerous procedures are put in place to increase
the efficiency and preservation of evidence collection at a crime scene.
As a trainee Crime Scene Officer (CSI), myself, and my team, were tasked with processing a
crime scene in Southport by request of the Merseyside Constabulary. At a crime scene, it is the
job of the CSI to identify, preserve, collect, and record potential evidence, thus making it
imperative that all present at the scene follow the same procedures for processing the evidence
and protecting themselves.
Crime scene procedures used to collect and record forensic evidence.
Restriction of access:
Before processing a scene, it is necessary to establish the boundaries and isolate the scene
depending on the crime committed and the amount of space determined to be of use in the
investigation. This is of vital importance to reduce the likelihood of the public contaminating
potential evidence or being unknowingly exposed to potential hazards.
These boundaries can be defined using a plastic, yellow barrier tape with the printed words
“Crime Scene - Do Not Enter,” This tape is simply wrapped around nearby objects or can be
defined using cones and is carried out by the First Attending Officer (FAO) as they are the first
on-site, thus have the best knowledge of potential evidence at the scene. Police barrier tape is
another tape used to define areas where the police are investigating, usually outside of the crime
scene. It is similar to the crime scene barrier tape but features a blue and white pattern instead,
along with “Police” in visible lettering.
The restriction of access would also include the use of a crime scene entry log to ensure that
only the necessary personnel are/were present at the crime scene to reduce potential
contamination of evidence.
Observation and recording, identifying, and targeting evidence:
An initial scene assessment is necessary when collecting evidence, as the conditions at the time
of retrieval will affect the state of the evidence. This assessment will be a mixture of notes,
photographs, video evidence, and any other forms of valid evidence present, such as equipment
to measure the temperature of the scene.
Notes should include the date/time of day to help identify the age and conditions of evidence
as well as the location/environment for similar reasons. External scenes may be impacted by
weather, such as snow and rain, making it more difficult for biological evidence and potential
physical evidence to be recovered—or make them easier to collect. A brief description of the
scene and packaged evidence collected will also aid in linking evidence retrieved to the crime
scene.
,“The photography of the crime scene should begin with wide-angle photos of the crime scene
and surrounding areas.” (Schiro, 2021) This will ensure that an accurate representation of the
crime scene is made available to those not present at the scene. Used in conjuncture with a plan
of the premises—a general sketch of the floor plan of the crime scene—will help illustrate the
layout of the scene, as well as linking evidence together.
Photographs and video recordings should include clear shots of evidence in situ in the event of
that evidence not being collected properly, but also to be used in comparison to known suspect
samples. After these photos have been obtained, secondary photos using a measuring ruler to
give the evidence in the photo scale must also be included. These images should also be labelled
to show their relevance to the investigation to any third party analysing the evidence.
Search patterns:
A plan of approach is necessary
when working in a team to
ensure that evidence is not
overlooked during collection.
Depending on the type of scene,
as well as the size, the search
patterns will vary, so choosing
the correct search pattern for the scene should be completed as soon as possible.
Making sure that everyone at the scene is following the pattern so there is no overlap of
evidence collection allows all the scene to be covered, minimising evidence loss.
“Larger areas are first divided into quadrants or zones so that each smaller area can be
scanned,” (How Forensics Experts Search a Crime Scene - dummies, 2021) after which,
smaller, defined areas can be examined using the above search techniques, though not limited
to them. For example, it may be more efficient to examine the length of a room or open location
instead of splitting it into quadrants or zones, depending on the size of the scene and team
present. Additionally, a spiral search pattern may not start from the centre of the crime scene
but, instead, from a point of interest, such as a pile of money, a murder weapon, or a body.
Limiting contamination:
Personal Protective Equipment (PPE) is required when entering a crime scene and will be
handed out by an entrance point to the scene to reduce potential risks to those present at the
scene and minimise contamination of evidence during collection.
PPE used includes hooded, disposable coveralls to protect yourself and your clothing, as well
as to cover your hair to prevent contamination of evidence. Goggles are also necessary for the
same reasons for your eyes, and masks reduce damage from breathing in chemical substances,
as well as environmental factors such as smoke.
Gloves are vital when collecting evidence as they reduce contamination and potential skin
contact with harmful substances. Fingerprints of those present may be left on evidence
collected, making a crime scene entry log even more vital in case of contamination.
Plastic covering for shoes is also important to reduce damage to the investigator’s shoes—and
stop them from being collected as evidence—as well as being another form of evidence for
examination as they can be turned inside out to preserve any collected trace evidence. Most
shoe covers are also skid resistant too, which would be extremely helpful if the scene were
particularly slippery.
Once the personnel have left the scene, their PPE will be packaged together and labelled as
evidence since there may be trace evidence on the PPE that was missed during collection, such
as gunshot residue or biological evidence on the gloves and shoe coverings. Evidence should
also be stored in separate locations if there is a risk of cross-contamination.
, Documenting trace materials:
When documenting collected trace evidence, it is especially important to ensure that the sample
is not exposed/contaminated, as that is likely the only evidence collected. Thus, ensuring that
the evidence is not contaminated after collection becomes even more important as the
likelihood of more of the evidence being recovered is low.
Ensuring that photographs of the trace materials are produced in the event of the evidence being
damaged or unwanted material is transferred to the evidence due to a lack of correct packaging.
In the same vein, a chain of custody is necessary not just for trace evidence, but any evidence
handled by multiple people.
The location this trace evidence was recovered from should also be included in any documents
as that can be as important as the evidence itself since trace evidence is often used to place a
suspect at a scene or to prove the usage of a weapon (gunshot residue, tool marks) or to prove
possession of illegal substances (drug samples). A sketch of the scene and photography must
be included when trace materials are discussed in a case to prove the validity of that trace
evidence.
Recovery of trace materials:
Correct methods of evidence collection must be used when recovering trace materials due to
their limited nature. It is lucky if there are more than a couple of opportunities to collect this
type of evidence at once.
Using more than one packaging layers may be advisable if the evidence is particularly loose or
easily exposed. A hair sample, for example, would be recovered with tweezers and placed in a
vial—which, by itself, is easily lost—but then placed inside of an evidence bag. This allows
any Criminal Justice Act (CJA) labels and continuation of evidence to be documented and kept
with the evidence instead of using a tag that may fall off in transit.
Trace materials may also be recovered from an investigator’s personal protective equipment
after handing it in—likely to be from the shoe cover or gloves—in the event of that material
having transferred onto the PPE.
In the case of evidence such as glass and drug samples, that can be potentially harmful, recovery
should be done using a spatula. Drug samples may then be placed in a plastic tube, sealed, and
placed into an evidence bag. Glass should be wrapped in paper and placed in a container with
other shards from the same area. These steps are done to ensure that the evidence is not
tampered with but also to make sure that the CSI collecting the evidence is not injured while
doing so.
A Common Approach Path (CAP) should be placed down before beginning to collect evidence
to ensure that everyone present follows the same path and to reduce the risk of contaminating
evidence by accidentally stepping on it. The CAP is not absolute and is only meant to provide
a secure passage through the main sections of the scene and can be exited, so long as caution
is taken to ensure that no evidence is damaged when you exit.
Characterisation and comparison of evidence:
Evidence is split into three categories: biological, chemical, and physical. These categories help
define the type of evidence collected as, for example, all biological evidence contains DNA,
so the techniques required for analysis and collection are different from those used for chemical
and physical evidence.
It is important to collect biological evidence as soon as possible as it will denature over time
and end up unable to be analysed. Depending on the scene—whether that is temperature,
exposure, or time—this evidence may be lost sooner, and potential chemical and physical
evidence is then put at risk. Physical evidence may also include recovered digital devices which
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