Crime Scene: Evidence
Collection & Protection
I. Assessing the Scene of the Crime
• The moment a police officer arrives on the
scene, a strict set of guidelines designed to
guard evidence against damage, contamination
or loss.
• Everything that occurs at the scene must be
documented.
• Failure to secure the scene could result in the
perpetrator walking free.
Primary and Secondary Crime Scenes
• A primary crime scene is where the crime actually
occurred.
– Typically yields the most useful evidence, but not
always
• A secondary crime scene is in some way related
to the crime but not where the crime took place.
– Sometimes the primary crime scene is not known and
investigators rely on clues from the secondary crime
scene to lead to the place the crime occurred.
Preserving and Processing the Crime
Scene
• 1. The boundaries of the crime scene must be
determined and cordoned off.
• 2. Only necessary personnel are permitted .
– First responding officer establishes a security log.
– Remember Locard’s Principal? Every person that
enters the scene leaves evidence of their presence
and could take away crucial evidence as they leave.
• 3. Preliminary walk-through examination
– Plans an approach to collection of evidence.
Documenting the Procedure
• Note Taker-Keeps an accurate account of all
activities around the crime scene.
– Detailed description of the scene
– Accurate list describing each piece of evidence
• When, where, and whom it was found by
• Who transported it to the lab
• Identifies and comments on every photo taken at the scene
• Photographer-Photos must be taken as soon as
possible before anything is moved to document
the scene in an unaltered condition.
Documenting the Procedure Cont.
– Photos of surrounding area of crime scene is
documented.
– Close-ups of each Item of evidence is taken, and
well as any injuries to the victim.
Documenting the Procedure Cont.
• Sketcher-Sketches show the relationship of each
item of evidence to other items or the body.
– Each piece of evidence is mapped to provide exact
graphic coordinates
– Sketches may be rough but need to be accurate, and
can be redrawn later for clarity
Example of a Crime Scene Sketch
Reconstruction of the Crime Scene
• At this point the investigator begins formulating
a hypothesis of the crime, focusing on the likely
sequence of events and the locations of
everyone present at the crime.
– Each piece of evidence must support the hypothesis
including the results from the crime lab.
– Reconstruction is an evolving process as more
evidence is found and other evidence is discredited.
– An investigator must at all times avoid making
assumptions.
Recognizing a Staged Crime
• Staging is when someone who’s committed a
crime attempts to make the scene look like
something that it isn’t.
– Making a murder look like a suicide
– Setting Fire to cover up another crime
– Breaking a window or prying a lock to confuse
entry.
II. Classifying the Evidence
• Evidence is anything that can be used to
determine whether a crime has been
committed
– Can link a suspect to the scene
– Can Corroborate or refute an alibi or statement
– Identify a perpetrator or victim
– Exonerate the innocent
– Induce a confession
Direct or Circumstantial Evidence
• Direct Evidence establishes a fact.
– Eyewitness statements and confessions
– Less reliable and more subjective
• Circumstantial Evidence requires a judge, and
or jury make an indirect judgment about what
happened.
– Fingerprints or DNA found at the scene matches
the suspects.
– More reliable and objective
Physical & Biological Evidence
• Forensic evidence can be divided into 2 basic
categories:
– 1. Physical Evidence
• Non-living or inorganic items
• Fingerprints, tool marks, fibers, drugs, bullets, explosives,
fire accelerants
– 2. Biological Evidence
• Includes organic material
• Blood, saliva, urine, hair, botanical materials
Associative Evidence
• Associative Evidence is evidence that either
associates or dissociates the suspect to the
crime scene.
Class and Individual Evidence
• Class characteristics are not unique to a particular
object, but place the particular bit of evidence into a
group of objects.
– Ex: Blood from the suspect found at the scene is
found to be ABO type B. Tens of millions of people
have this type and could be the possible suspect.
• Individual characteristics narrow down the evidence to
one person or small group of individuals.
– EX: Blood from the suspect found at the scene is put
through a DNA fingerprint test will narrow the
possible suspects down to one person
Analyzing the Evidence at the
Crime Scene
• 2 Purposes:
– 1. Identification
• Determines what the item or substance is
– 2. Comparison
• Find out if a known and a suspect item or substance
share a common origin
• Linkage-A connection between a suspect and
a person, place or object
– Connections formed by evidence
III. Collecting the Evidence
• Searching the area
– The way the investigator searches an area
depends on its size and physical layout
– Investigators typically follow a geometric pattern
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•
•
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Criss-Cross Grid,
Shoulder to shoulder linear pattern
Spiral pattern is used when expnding out from a body
Zones are used for large areas
Gathering Evidence
• Investigators start with evidences that is the
most fragile, or is at risk of being lost.
– Blood, fibers, hair, fingerprints……
• Techniques for gathering fragile evidence
– Fingerprints are photographed and then lifted
– Tool marks, shoeprints, and tire tracks are
photographed and the a cast is made
– Hairs are found using alternative light source and
gathered with tweezers.
Packing the Evidence
• Dry trace evidence is packed in druggist’s
folds or small folded papers.
• Documents are sealed in plastic covers.
• Liquid evidence is put into unbreakable
airtight, sealed containers.
• Wet biological evidence such as a bloody shirt
is dried to prevent bacterial or mold growth.
• Tool marks and bullet holes are processed at
the scene
Chain of Custody
• Continuous records showing that evidence has
been kept safe and secure from the crime
scene to the lab is vital to the case.
• Every person that handles a piece of evidence
must be accounted for and properly recorded.
• A break in the chain of custody could render
the evidence inadmissible by compromising its
integrity.
Chain of Custody Cont.
• Each person who accepts an item of evidence initials and
dates it, and then is responsible for maintaining its
integrity until it is passed on to the next person.
• Police officer finds a shell casing at the scene….
– Collects it, marks it, places it in an evidence bag, then signs it
over to an investigator
– Investigator signs it over to the lab technician who runs the
necessary tests.
– Technician then signs it over to the custodian of evidence
(Police officer in charge of the secured evidence lock-up area at
the police department).
– From there it will be signed over to the prosecuting attorny for
presentation in court.