Chapter 2
Johnston High School
Forensics

Learning Goals
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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

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

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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?

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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???

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Multiple views
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Entrances
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Exits
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Windows
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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

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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
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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

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Goal: handle evidence so that there is least amount of change from CS to lab
Potential problems
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Contamination
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Breakage
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Evaporation
Accidental scratching/breaking
Loss via carelessness
Integrity = evidence kept intact (ex. Hair, soil should be left on clothing)

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If evidence is found on large structure (door, wall)…
 remove specimen with forceps
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With blood, scrape off surface, transfer to moistened swab, or cut out area bearing stain

Most Important Point About
Evidence Collection
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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

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
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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
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Each person may be required to testify in court
If not, authenticity and integrity of evidence is lost

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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
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Can also be obtained from victim
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Paint from a hit-and-run vehicle

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
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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
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Can’t ship certain chemicals/live ammo/explosives
Need evidence submission form
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Nature of crime, victim, case#, agency, investigator
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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 1 st 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
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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…
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Location of body
Size of body
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Victim’s clothing
Weather condition

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