The Crime Scene
Chapter 2
Johnston High School
Learning Goals
Define physical evidence
Discuss responsibilities of first officer
arriving at scene
Explain steps to be taken to thoroughly
record crime scene
Describe proper procedures for
conducting systematic search for
More learning goals…
5) Describe proper techniques for packaging
common types of physical evidence
6) Define and understand concept of chain
of custody
7) Understand contributions of the forensic
pathologist, entomologist, and
anthropologist can make to a homicide
Physical Evidence
Physical Evidence: Any object that can
establish that a crime has been committed
or can link a crime to its victim or its
Importance of Evidence
Forensic Science begins at the crime
Scientist must be able to RECOGNIZE
Must be able to COLLECT evidence
Must be able to PRESERVE evidence
Remember…garbage in, garbage out!
Approaching a Crime Scene
Securing and Isolating
Crime Scene
The first officer at the scene must…
1) offer medical assistance when needed
and/or make an arrest
2) exclude all unauthorized personnel from
scene (very hard!)
3) Call for assistance/backup
4) isolate area (tape, barricades)
Must try to preserve and protect area as much
as possible
Once Secured…
 Lead
investigator evaluates area
 Determines boundaries
 Establishes perpetrator’s path (entry
and exit)
 Obvious evidence documented and
 Initial walk-through & develop
strategy for examination
Recording the Scene
Limited time to work in CS in untouched
Records useful for investigation/court
What are some methods of recording the
crime scene?
Recording the Crime
 Photographs
 Sketches
 Notes
Take unaltered!
Do not move evidence until picture is taken!
If moved, must be recorded in notes
All photos must show position and location to
crime scene
Close ups of smaller items must be taken
Use a ruler or scale to note size
 Scene
 Multiple
 Entrances
 Exits
 Windows
Close ups
After photographing…make a rough sketch
Drawn at crime scene
Contains accurate depictions of dimensions of
scene (use tape measurer)
Shows location of all objects having bearing
on the case
Finished Sketch
Done carefully, attention to appearance
Must reflect rough sketch (admissible in
Computer Aid Drafting (CAD) -software for
Drawn to scale
Rough Sketch to Final
Rough vs Finished Sketch
Match to sketch
Constant activity
Quick, short, bulleted
What can you not see from the photo?
Helpful for long-term cases - memory
Identifies all evidence – what is it? Who
Tape recording used sometimes
What should be noted?
These notes must identify:
Time an item of physical evidence was
Who discovered it?
How and by whom it was packaged and
Disposition of an item after it was collected
May be the only source of information for
refreshing one’s memory
The Search – Part 1
The search for physical evidence at a crime
scene must be thorough and systematic.
The search pattern selected will normally
depend on the size and locale of the scene and
the number of collectors participating in the
For a factual, unbiased reconstruction of the
crime, the investigator—relying upon his or her
training and experience—must not overlook any
pertinent evidence.
Physical evidence can be anything from massive
objects to microscopic traces.
Search Patterns
The Search – Part 2
Often, most evidence is clearly visible, BUT…
Others can only be detected via examination in the
Must collect ALL possible carriers of trace
Vacuum sweepings
Rug samples
Fingernail scrapings
Beyond the Crime Scene
Search for evidence must extend to
autopsy room
Medical examiner – determine COD
Tissues and organs retained for
pathological and toxicological examination
Medical examiner secures a variety of
items for investigator
Evidence the ME sends to
Victim’s clothing
Fingernail scrapings
Head and pubic hairs
Blood (for DNA analysis)
Vaginal, anal, and oral swabs (sex-related
Recovered bullets from body
Hand swabs from shooting victims (GSR)
Interactive Autopsy Assignment
Go to this website and answer questions
Click on Interactive Autopsy to the right of
the screen
Collecting & Packaging
Goal: handle evidence so that there is least
amount of change from CS to lab
Potential problems
 Contamination
 Breakage
 Evaporation
 Accidental scratching/breaking
 Loss via carelessness
Integrity = evidence kept intact (ex. Hair, soil
should be left on clothing)
 If
evidence is found on large
structure (door, wall)…
remove specimen with forceps
 With blood, scrape off surface,
transfer to moistened swab, or cut
out area bearing stain
Most Important Point About
Evidence Collection
 Each
different item or similar
items collected at different
locations must be placed in
separate containers!
Prevents damage through contact
Prevents cross contamination
Collecting Evidence
Tools for Evidence Collection
Forceps (to pick up small items)
Unbreakable plastic pill bottles w/
pressure lids
Hairs, glass, fibers, other small trace evidence
Manila envelopes, screw-cap glass vials,
metal/cardboard pill boxes also good for
trace evidence
Small trace evidence and
miscellaneous evidence
Ordinary mailing envelopes should be
Druggist folds are often used for small
Folding paper to produce closed container,
keeping specimen inside
Sealable plastic bags often universal
2 Exceptions to the Rule
Bloodstained materials
Do NOT store in airtight containers!
Moisture builds up and allows for mold growth
Destroys evidentiary value of blood
Use breathable paper envelopes or bags
All clothing must be air dried and placed
individually in separate bags
Charred debris from a fire MUST be placed in
airtight container to prevent evaporation of
volatile petroleum residues
Chain of Custody
Chain of Custody = a list of all people who came
into possession of an item of evidence
Must be established for use in court
Everyone must be accounted for!
Each person must obtain written record of acquisition
and disposition
Each person may be required to testify in court
If not, authenticity and integrity of evidence is
Standard/Reference Samples
Standard/Reference Sample: Physical
evidence whose origin is known, such
as blood or hair from a suspect, that
can be compared to crime-scene
Can also be obtained from victim
 Paint from a hit-and-run vehicle
Other Controls
Buccal Swab – swab from the inner portion of
the cheek, performed to collect cells for use in
determining the DNA profile of an individual
Substrate Control
Uncontaminated surface material close to area where
physical evidence has been deposited
Used to ensure that the surface on which a sample
has been deposited does not interfere with lab results
Used in arson cases – has surface been exposed to
Submit Evidence to Lab
Delivered personally or by mail depending on
case and urgency
Person familiar with case
Can’t ship certain chemicals/live ammo/explosives
Need evidence submission form
Nature of crime, victim, case#, agency, investigator
Brief description of case
List of evidence
What to investigate for each time
Evidence Submission Form
Murder Scene: Death and
Questions a forensic pathologist may ask:
Who is the victim?
What injuries are present?
When did the injuries occur?
How and why were injuries produced?
Determining COD is primary role. If not known
externally, AUTOPSY is performed: Medical
dissection post-mortem to determine COD.
Review on Estimating TOD
Rigor Mortis: Post mortem condition that results
in the stiffening of muscle mass
Manifests within 1st 24 hours; disappears within 36
Livor mortis: Post mortem condition that results
in the settling of blood in areas closest to
Skin appears blue/purplish
Begins immediately after death and continues for up
to 12 hours after death
Was the victim’s position changed after death?
Review on estimating TOD
Algor Mortis: Process by which the body
temperature continually cools after death
until it reaches the ambient temperature
Beginning about 1 hour post mortem,
body loses 1-1.5 degrees F per hour
Rate of heat loss depends on…
Location of body
 Size of body
 Victim’s clothing
 Weather condition
Another way to determine TOD
Determine potassium (K+) levels in the
ocular fluid in the eye (aka vitreous
After death, cells in the inner surface of
eyeball release K+ into ocular fluid
Use rate of release of K+ to determine
Also…food in stomach = last meal
Forensic Anthropology
Identification of human skeletal remains
Bones are extremely durable and undergo
slow breakdown
Provide individual characteristics: sex,
age, race, injury
Create facial reconstruction – to help ID
Help ID in mass disaster
Forensic Anthropology
Forensic Entomology
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