Transcript The Crime Scene

The Crime Scene
Chapter 2
Johnston High School
Forensics
Learning Goals
1)
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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
evidence
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
investigation
Physical Evidence
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Physical Evidence: Any object that can
establish that a crime has been committed
or can link a crime to its victim or its
perpetrator.
Importance of Evidence
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Forensic Science begins at the crime
scene!
Scientist must be able to RECOGNIZE
evidence
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
photographed
 Initial walk-through & develop
strategy for examination
Recording the Scene
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Limited time to work in CS in untouched
state
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Records useful for investigation/court
What are some methods of recording the
crime scene?
Recording the Crime
Scene
 Photographs
 Sketches
 Notes
PHOTOGRAPHY
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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
Videotaping???
Photography
 Scene
 Multiple
views
 Entrances
 Exits
 Windows
Evidence
Close ups
Perspectives
Multiple
angles
Sketches
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After photographing…make a rough sketch
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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
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Done carefully, attention to appearance
Must reflect rough sketch (admissible in
court)
Computer Aid Drafting (CAD) -software for
reconstructing
Drawn to scale
Rough Sketch to Final
bsapp.com
Rough vs Finished Sketch
Notes
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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
collected?
Tape recording used sometimes
What should be noted?
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These notes must identify:
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Time an item of physical evidence was
discovered
Who discovered it?
How and by whom it was packaged and
marked
Disposition of an item after it was collected
May be the only source of information for
refreshing one’s memory
The Search – Part 1
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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
search.
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
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Often, most evidence is clearly visible, BUT…
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Others can only be detected via examination in the
lab
Must collect ALL possible carriers of trace
evidence
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Clothing
Vacuum sweepings
Rug samples
Fingernail scrapings
Beyond the Crime Scene
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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
Investigator
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Victim’s clothing
Fingernail scrapings
Head and pubic hairs
Blood (for DNA analysis)
Vaginal, anal, and oral swabs (sex-related
crimes)
Recovered bullets from body
Hand swabs from shooting victims (GSR)
Interactive Autopsy Assignment
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Go to this website and answer questions
(given)
http://www.hbo.com/autopsy/interactive/
Click on Interactive Autopsy to the right of
the screen
Collecting & Packaging
Evidence
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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
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Most Important Point About
Evidence Collection
 Each
different item or similar
items collected at different
locations must be placed in
separate containers!
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Prevents damage through contact
Prevents cross contamination
Collecting Evidence
Bag
&
Tag
Tools for Evidence Collection
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Forceps (to pick up small items)
Unbreakable plastic pill bottles w/
pressure lids
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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
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Ordinary mailing envelopes should be
avoided
Druggist folds are often used for small
trance
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Folding paper to produce closed container,
keeping specimen inside
Sealable plastic bags often universal
container
2 Exceptions to the Rule
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Bloodstained materials
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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
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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!
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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
lost
Collecting
Standard/Reference Samples
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Standard/Reference Sample: Physical
evidence whose origin is known, such
as blood or hair from a suspect, that
can be compared to crime-scene
evidence
Can also be obtained from victim
 Paint from a hit-and-run vehicle
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Other Controls
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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
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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
accelerant?
Submit Evidence to Lab
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Delivered personally or by mail depending on
case and urgency
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Person familiar with case
Can’t ship certain chemicals/live ammo/explosives
Need evidence submission form
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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
Autopsies
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Questions a forensic pathologist may ask:
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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
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Rigor Mortis: Post mortem condition that results
in the stiffening of muscle mass
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Manifests within 1st 24 hours; disappears within 36
hours
Livor mortis: Post mortem condition that results
in the settling of blood in areas closest to
ground
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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
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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
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Rate of heat loss depends on…
Location of body
 Size of body
 Victim’s clothing
 Weather condition
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Another way to determine TOD
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Determine potassium (K+) levels in the
ocular fluid in the eye (aka vitreous
humor)
After death, cells in the inner surface of
eyeball release K+ into ocular fluid
Use rate of release of K+ to determine
TOD
Also…food in stomach = last meal
Forensic Anthropology
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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