FORENSIC
SCIENCE
INTRODUCTION
Crime Scene
Investigation
Forensic Science
Definition:
 The application of science to those criminal
and civil laws that are enforced by police
agencies in a criminal justice system.
 The business of providing timely, accurate,
and thorough information to all levels of
decision makers in our criminal justice
system.
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Complex Reasoning
In Forensic Science
 Deductive and
Inductive Reasoning
 Classifying
 Comparing and
contrasting
 Problem Solving
 Analyzing Perspectives
 Constructing Support
 Error Analysis
CRIME
Why Did It
Happened?
What
Happened?
Crime Scene
Evidence Collection
Witness, Suspect and
Motive Development
Post Scene
+
Investigative Stage
Profiling
Means
Motive
Opportunity
Who Did
It?
=
Identification
and Arrest of
Suspect
Evidence Processing
Cause, manner, time
of death
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CORPUS DELICTI
You must prove:
“Body of the Crime”
 that a crime occurred
 that the person charged with the crime was responsible for the crime
Top Reasons for Committing a Crime
 Money
 Revenge
 Sex
 Emotion--love, hate, anger
Source of Evidence
 Body
 Primary and/or Secondary Crime Scene
 Suspect(s)
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Crime Scene Team
A group of professionals investigators, each trained in a variety
of special disciplines.
Team Members






First Police Officer on the scene
Medics (if necessary)
Investigator(s)
Medical Examiner (if necessary)
Photographer and/or Field Evidence Technician
Lab Experts:
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
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First Officer
at the Scene
A
Assess the crime scene
D
Detain the witness
A
Arrest the perpetrator
P
Protect the crime scene
T
Take notes for CSI team
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Eye Witness
Faces Composite Program
by InterQuest
 Will explain their part of the
scene
 Give enough information to
lead the team to a conclusion
about what happened at this
crime scene
“Perception is reality.”
 As a result an eye witness may
not be the best source of crime
scene information.
 A police composite may be
developed from the witness
testimony by a computer
program or forensic artist.
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Basic Stages in a Search
These are the responsibility of the 1st Officer
at the scene.
Approach, secure and protect the scene
Initiate preliminary survey/determine scene boundaries
Only authorized personnel should be allowed on the scene
(Every person who enters the scene is a potential contaminator of viable
physical evidence)
Once a scene is secured, the lead investigator duties:
Evaluate physical evidence possibilities
Prepare narrative description
Depict scene photographically
Prepare diagram/sketch of scene
Conduct detailed search
Record and collect physical evidence
Conduct final survey
Release scene
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Photography
Scene should be photographed in an unaltered
condition. Unless someone is injured, everything
should be left in its unaltered condition.
Close-up of phys. evidence should include a ruler or
something to show size/scale
Videotaping/digital cameras
Still photography is still the best for its detail
WHAT to photograph?
Area of crime
Adjacent areas
Entrance/exit
Body if present -- area under body after removal
injuries/ weapons
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ROUGH
Sketches
After photos, sketch… first rough sketch is made at
the scene
Accurate depiction of the dimensions at the scene
Location of important objects to the case
TRIANGULATION METHOD – measured accurately
Each object is given a letter and a legend or list will
correlate the letter to the item
Designate north on the sketch
( The finished sketch is drawn to scale using the
measurements provided in the rough sketch and is
used as court evidence)
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HOW do you do a proper sketch?
Lay out basic perimeter
Windows, doors, etc…
Set forth fixed objects, furniture, etc…
Record position of evidence
Appropriate measurements – double check
Key/legend, compass orientation, etc…
NOTES:
Constant activity throughout the processing of the scene
Detailed description of the scene with location of evidence
recovered
Must id the time the evidence was discovered, whom, how,
and then packaged, marked after collected
Tape recording notes is helpful, but would need to be
transcribed.
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Typical material found on rough sketch
Specific location Date
Time
Case identifier
Preparer
Weather
conditions
Lighting
conditions
Scale or
disclaimer
Compass
orientation
Evidence
Measurement
Key or legend
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Crime Scene
Sketch
Date: August 14, 2001
Time: 11:35
Criminalist: Ann Wilson
Location: 4358 Rockledge Dr
St. Louis, Mo.
A. Couch/sofa
E
c
B. Female body
D
C. Knife
D. Over turned Lamp
E. Chairs
E
F. Table
G. Fireplace
G
A
F
E
E
E
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TRIANGULATION
Measure from A to
B and then to the
evidence in a
triangular shape.
A+B need to be
fixed points,
something that will
not change!
Examples of a
fixed point:
- windows
- doors
- trees
- buildings
MAPPING
TECHNOLOGY
The latest technology
includes this Nikon
Tsunami with
computer. The exact
location of all crime
evidence can be
determined and
directly loaded into a
computer to produce a
crime scene map.
(Cost = $35,000 for the set)
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Can we search for evidence
now?
Edmond Locard - French professor
Considered the Father of Criminalistics
Built the world’s first forensic laboratory in
France in 1910
Locard Exchange Postulate:
Whenever two objects come into contact
with each other, traces of each are
exchanged.
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FOUR BASIC PREMISES
The best search options are typically the most
difficult and time consuming
You can not “over document” the physical
evidence.
There is only one chance to perform the job
properly
There are two basic search approaches:
A “cautious” search of visible areas, taking steps
to avoid evidence loss or contamination
After the “cautious” search, a vigorous search for
hidden/concealed areas.
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The Search….
• A search must always be thorough and systematic
(even if a suspect is guilty!)
• Methods of search are always customized to suit the
crime. (Ex. Large open area uses a line search with
a few people)
• Here are some factors that help determine the type
of search method:
- Locale and size of area
- # of techs available
- size/type of evidence
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Crime Scene
Search Patterns
TWO of FOUR PATTERNS
Strip or Line
Quadrant or Zone
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Crime Scene
Search Patterns
TWO of FOUR PATTERNS
Spiral
Grid
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Collection…
• The collection of evidence starts with the most
fragile or most easily lost evidence.
• Photographs are continually taken.
• Most items are placed in paper envelopes or bags.
• Any liquid, arson evidence, or moist evidence are
packaged differently, not in paper bags.
• Items are always packaged separately to eliminate
cross-contamination.
• Proper labeling must always be place on ALL
packages!
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WHAT GOES TO THE LAB?
Physical evidence must be collected in such a way that prevents
any change between the crime scene and the crime lab.
 Victim’s clothing- never in an airtight container.
 Fingernail scrapings
 Hairs- leave on the article and send entire article to lab, where they will remove the hair
 Blood- leave on the article and send entire article to lab, where they will remove the blood
 Never in an airtight container, because the condensation could cause mold growth which could destroy the evidence.
 Fibers- leave on the article and send entire article to lab, where they will remove the fibers
 Swabs of secretions
 Charred debris- should be packaged in an air-tight container, so the petroleum residues
do not evaporate. (paint cans)
 Bullets
 Hand swabs if needed
NOTE: Each different item must be packaged separately!
(prevent cross contamination)
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Just A Thought…
It’s not what you know
that hurts you, its what
you think you know
and it’s not so
.
. . . .Mark Twain
How does this apply to
forensic science and crime
investigations?
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