 Conducting a Systematic Search for Evidence
 Various Types of Evidence
 Collecting and Packaging Physical Evidence
 Steps to a Crime Scene
 Terms to Know
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Forensics begins at the Crime Scene!
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If the investigator cannot recognize physical
evidence or cannot preserve it for the
laboratory examination then the case could
fall through.
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CORPUS DELICTI
“Body of the Crime”
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You must prove:
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Top Reasons for Committing a Crime
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that a crime has occurred
that the person charged with the crime was responsible for the
crime
Money
Revenge
Sex
Emotion--love, hate, anger
Source of Evidence
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Body
Primary and/or Secondary Crime Scene
Suspect(s)
What is Physical Evidence?
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Any object that can establish that a crime
scene has been committed or can provide a
link between a crime and its victim or
between a crime and its perpetrator.
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What is the value of Physical Evidence?
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It can prove that a crime has been committed and
set the scene for the investigation.
It can back up witness or prove it false.
It can link a suspect with a victim or with a crime
scene.
It can determine the identity of people associated
with a crime.
It can allow investigators to reconstruct a crime.
Evidence
Characteristics
Class - common to a group of objects or persons; a
group of objects that share properties or
characteristics (this evidence considered mainly
circumstantial)
Individual - can be identified with a particular person or
single source.
ABO Blood Typing
Blood DNA Typing
Evidence
Transient Evidence –
1.
temporary, easily changed or
lost, usually observed by the first
officer at the scene
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Odor - putrefaction, perfume,
gasoline, urine, burning, explosives,
cigarette or cigar smoke
Temperature - of room, car hood,
coffee, water in a bathtub; cadaver
Imprints and indentations footprints; teeth marks in perishable
foods; tire marks on certain surfaces
Markings
Evidence
Pattern or Transfer Evidence produced by direct contact
between a person and an object
or between two objects. There
are several ways of classifying
evidence. In this class, we will
use:
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Biological
Chemical
Physical
Miscellaneous
Biological Evidence
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Blood
Semen
Saliva
Sweat/Tears
Hair
Bone
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Tissues
Urine
Feces
Animal Material
Insects
Bacterial/Fungal
Chemical Evidence
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Fibers
Glass
Soil
Gunpowder
Metal
Mineral
Narcotics
Drugs
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Paper
Ink
Cosmetics
Paint
Plastic
Lubricants
Fertilizer
Physical (impression)
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Fingerprints
Footprints
Shoe prints
Handwriting
Firearms
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Printing
Number restoration
Tire marks
Tool marks
Typewriting
Miscellaneous
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Laundry marks
Voice analysis
Polygraph
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Photography
Stress evaluation
Psycholinguistic
analysis
Vehicle identification
Evidence
Conditional Evidence - produced
3.
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by a specific event or action;
important in crime scene
reconstruction and in determining the
set of circumstances within a
particular event.
Light--headlight; lighting
conditions
Smoke--color, direction of travel,
density, odor
Fire--color and direction of the
flames, speed of spread,
temperature and condition of fire
Evidence
Conditional Evidence (cont.)
• Location--of injuries or wounds; of bloodstains; of
the victims vehicle; of weapons or cartridge cases;
of broken glass, etc.
• Vehicles--doors locked or unlocked, windows
opened or closed; radio off or on (station); odometer
mileage
• Body--position; types of wounds; rigor, livor and
algor mortis
• Scene--condition of furniture, doors and windows;
any disturbance or signs of a struggle.
Steps to a Crime Scene:
1.
Secure and isolate the crime scene.
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Done by the 1st officer on the scene.
Lead investigator evaluates the site.
Set the boundaries of where the crime occurred.
Locate where the perpetrator entered and exited
the scene.
Conduct a systematic examination of the scene.
Record the scene. (photos/sketches/notes)
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Crime Scene Team
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A group of professionals investigators, each trained in a variety of
special disciplines.
Team Members
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First Police Officer on the scene
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Medics (if necessary)
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Investigator(s)
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Medical Examiner (if necessary)
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Photographer and/or Field Evidence Technician
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Lab Experts
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pathologist
DNA expert
forensic odontologist
forensic psychologist
firearm examiner
document and handwriting experts
serologist
toxicologist
forensic anthropologist
forensic entomologist
bomb and arson expert
fingerprint expert
Photographing a Crime Scene
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Photos are taken at different angles to get a clear view of the scene.
If items/people are removed that should be noted on the photo.
Photographs are taken of all the physical evidence that is collected.
Digital cameras are the best since you can piece together several
pictures for a 3D view.
Video cameras are good for the added bonus of sound records.
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Sketching a Crime Scene
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Rough Sketch
 Draft representation of all the essential information
and measurements at a crime scene. Drawn at the
scene.
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Finished Sketch
 Precise drawing of a crime scene drawn to scale.
(Drawn with care)
 Use of computer CAD programs is most common.
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Rough Sketch
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Finished Sketches
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Conducting a Systematic Search for
Evidence
Spiral Search
Grid Search
Start
Finish
Strip / Line Search
Quadrant / Zone Search
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Conducting a Systematic Search for
Evidence
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After the search is conducted at the scene
more evidence can be collected off of the
suspects.
If there is a dead body evidence is looked for
on their clothing, fingernail shavings,
head/pubic hairs, vaginal/anal/oral swabs,
and hand swabs for GSR.
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Collecting and Packaging Evidence
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Must be done correctly and accurately to
maintain the integrity so that the evidence
can prove the case.
Each piece of evidence must be separately
collected and packaged
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Collecting and Packaging Evidence
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Chain of Custody
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List of all the people who came
in possession of an item of
evidence.
This is very important when
establishing validity in a court
case.
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Collecting and Packaging Evidence
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Standard / Reference Sample
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Physical Evidence whose origin is known and can be
compared to an unknown.
 Examples:
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Soil from a known source vs soil from crime scene.
DNA from a suspect vs DNA from crime scene.
Substrate Control
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Used mainly in arson cases. A piece of unmarked material
is used to compare to the marked material.
 Example:
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A burnt piece of countertop is compared to an non-burnt
piece of the table top.
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Terms to Know:
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Buccal swab
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Chain of Custody
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Finished Sketch
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Rough Sketch
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Physical Evidence
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Standard/Reference Sample
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Substrate Control
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