Transcript FORENSIC SCIENCE - Forensic Science at HCTC

Types of Evidence
Types of Evidence
Objectives
You will understand:
The value of indirect and direct evidence in a
court of law.
That eyewitness accounts have limitations.
What physical evidence can and cannot prove
in court.
That the forensic scientist’s main goal is to find a
unique source for the evidence.
You will be able to:
Explain the difference between indirect and
direct evidence.
Describe what is meant by physical evidence
and give examples.
Distinguish individual evidence from class
evidence.
Determine the significance of class evidence.
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Types of Evidence
5 questions Lawyers should NEVER ask a
witness in court:
1. Is it true that you were present until you left the building?
2. Who was it that got killed in the accident - you or your sister?
3. When the two cars collided, how far away from each other were they?
4. Was that the first time that your brother had committed suicide?
5. When he took your photo, were you present?
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Learning Targets
Distinguish between testimonial and physical
evidence.
What factors influence the reliability of
eyewitness testimony?
What methods improve accuracy of an
eyewitness identifying a suspect correctly?
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Types of Evidence
Classification of Evidence
Testimonial evidence is a statement made
under oath; also known as direct evidence or
prima facie evidence.
"at first face" or "at first appearance"
Physical evidence is any object or material that
is relevant in a crime; also known as indirect
evidence. Examples are hair, fiber, fingerprints,
documents, blood, soil, drugs, toolmarks,
impressions, glass.
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What kind of evidence is a
fingerprint?
Physical
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What kind of evidence is a
bitemark?
Physical
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What kind of
evidence is
DNA?
Physical
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What kind of evidence is this?
Testimonial
Video
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What is testimonial evidence?
Testimonial evidence includes oral or written statements given to
police as well as testimony in court by people who witnessed an
event.
Eyewitness accounts can be a useful tool in helping investigators
with analyzing a crime scene, but are not viewed to be highly
reliable. In addition, eyewitness identifications (right or wrong) can
have a big influence on the outcome of an investigation or trial.
People are likely to view the same scene in different ways
depending on their positions, line of sight, familiarity with the area,
and other factors that can interfere with a person’s ability to
remember details.
Memory Challenge
Directions:
You will have 30 seconds to view the next screen.
Try to memorize all 20 items you see!
You are NOT allowed to write anything down
You CANNOT talk to anyone else.
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Items to remember ...
Neuroscience for Kids - http://faculty.washington.edu/chudler/puzmatch1.html
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What do you remember?
You have 2 minutes to list as many of the items as you can!
How did you do?
All 20 – Awesome
15-19 – Great
10-14 – Pretty swell
5-9 – Could be better
4 or Less – Wake up
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Selective Attention
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Consider the Following
Observe the following image.
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What color was the car to the left of the stop
sign?
What type of vehicle was sitting at the right of
the stop sign?
What color was the vehicle on the right?
Which way was the stop sign facing?
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Types of Evidence
Reliability of Eyewitness
False Memory Experiments
 Renowned psychologist Elizabeth Loftus conducted false memory
experiments. In this experiment, subjects were shown an image of a car
near an intersection.
 The researchers asked the subjects who had seen the yield sign questions
that deliberately included the words "stop sign." Researchers did the
opposite with subjects who were shown the stop sign image.
 Results of this experiment showed that subjects created false memories as
they recalled not the image they had seen but rather the information that
had been implanted.
 http://www.ehow.com/info_7935459_forensic-psychology-experiments.html
video
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The Bunny Effect
The Bunny Effect
CBS News Video
Types of Evidence
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False Memories (balloon ride)
video
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Video
Test
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Jennifer Thompson’s
The Innocence Project-CBS 60 Minutes
60 Minutes Part 2
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Types of Evidence
Reliability of Eyewitness
Factors that affect accuracy:
Nature of the offense and the situation in which
the crime is observed
Characteristics of the witness
Manner in which the information is retrieved
Additional factors:
Witness’s prior relationship with the accused
Length of time between the offense and the
identification
Any prior identification or failure to identify the
defendant
Innocence Project > 5:23
Any prior identification of a person other than the
defendant by the eyewitness
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Did you know?
Types of Evidence
According to The Innocence Project (2008)
"Eyewitness misidentification is the single greatest
cause of wrongful convictions nationwide, playing a
role in more than 75% of convictions overturned
through DNA testing." Still, the criminal justice
system profoundly relies on eyewitness identification
and testimony for investigating and prosecuting crimes
(Wells & Olson, 2003).
What factors affect a person’s memory
and their ability to identify a suspect?
Let’s do a little research!
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Source: http://www.helium.com/items/1276135-accurate-eyewitness-accounts
Witness Factors
Types of Evidence
Age may play a role in the
accuracy of an eyewitness’
statement or identification of a
suspect. Studies have shown that
when a lineup contains the actual
culprit, both young children and
elderly perform well, but when the
lineup does not contain the culprit
there is a higher rate of mistaken
identifications.
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Source: http://www.helium.com/items/1276135-accurate-eyewitness-accounts
Types of Evidence
The race of the
witness may also play a
role. The Cross Race
Effect (CRE) is a
phenomenon in which
people are better at
recognizing faces of
their own race rather
than those of other
races.
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The use of drugs can
alter a person’s
ability to recall the
events of a crime
even after they are
no longer under the
influence.
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 A person’s memory of an
event can be influenced by
other witnesses,
investigators, and/or the
media. Investigators use
open-ended questioning and
follow procedures for
conducting line-ups to limit
their influence on a witness’
memory of an event or
identification of a suspect.
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Evidence & Suspect Factors
Crime
A crime that is extremely
traumatic for an eyewitness
may affect his/her recall of
the event.
Ex.: a witness confronted
with a weapon tends to
focus on the weapon rather
than the perpetrator’s face.
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Source: http://www.helium.com/items/1276135-accurate-eyewitness-accounts
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Someone who is able to
focus on a perpetrator's
face for a minute or
longer will tend to have
a more accurate
memory than someone
who saw the person for
only a few seconds.
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 Studies have shown that faces
that are either highly attractive,
highly
unattractive,
or
distinctive are more likely to
be accurately recognized.
Simple disguises, such as hats
or sunglasses, can interfere
with
accurate
eyewitness
identification. However, body
piercings and tattoos increases
the likelihood of an accurate
identification.
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 The time of day in which the
crime occurred as well as a
person’s view of the scene
may affect what a he/she is
able to see.
 In addition, a person who is
familiar with the area in which
the crime took place, may have
a better recall of the positions
of the victims or suspects.
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Crime Scene Challenge
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Now that your eyes and brain are warmed up, let’s
test your observation skills a bit more.
You will have 2 minutes to study the photograph of a
crime scene on the next slide.
Try to pay attention to details as you will be asked 10
questions about the crime scene!
You are not allowed to write anything down until
after the time is up.
Ready?
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Answer each question below.
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1. What color coffee mug was in the picture? Blue
Red
Yellow
2. When was the deadline? Yesterday
Today
Tomorrow
3. What time was on the clock on the wall? 10:40
11:05
1:55
4. How many sticky notes were on the whiteboard? Four Six Eight
5. Which of the following was NOT in the picture? Stapler Trash Can
6. What was the name on the plaque on the desk?
7. What color was the victim's shirt?
Black
8. How many plants were in the picture?
None
Bill
Blue
Source: http://forensics.rice.edu/html/picture_begin.html
Carl
Red
One
9. What was the color of the marker in the desk drawer?
10. Where was the book in the picture? On a box
Brian
Printer
Two
Red
Blue
Green
In the trash can Under the body
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Facial Composites
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Investigators work with sketch artists and eyewitnesses to create
facial composites, or sketches of a person’s face. Today many
police departments are using facial reconstruction software to
help them with this task.
The composite may be used internally to assist officers in
identifying the suspect or used externally through local media
(radio, TV, and newspaper) to solicit leads from citizens.
FACES – A software
program that offers many
options to help you
recreate a person’s facial
features.
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Types of Evidence
Eyewitness
New technology is helping
eyewitnesses to be able
to describe suspects.
A police composite may be
developed from the
witness testimony by a
computer program or
forensic artist.
DEMO
FACES—a composite
program by InterQuest
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You will need a calculator in a
day or two! Make sure you have
one. (Was on your supply list)
Types of Evidence
Physical Evidence
As a result of the
influences on
eyewitness memory,
physical evidence
becomes critical.
Identity and origin
of physical evidence
is main task of
forensic scientist.
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Forensic scientists consider
the chemical and physical
properties of materials they
are investigating.
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Physical Properties
Definition:
anything you can
observe or
measure without
changing the
chemical identity
of the substance







Length
Shape
Color
Temperature
Density
Hardness
Solubility [what it
dissolves in]
 Refractive index [how
substance bends light]
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Types of Evidence
Physical Changes
Changes in physical properties
Chemical composition doesn’t change
Tearing a piece of paper
Dissolving salt in water
Denting your car
Spilling milk
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Types of Evidence
Can be
observed when
the substance
changes its
chemical
composition
Chemical Properties
Reactivity with :
 Air (Flammability or
oxidizing ability)
 Water
 Acid
 Base
Sample may be
destroyed during testing
VIDEO
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Types of Evidence
Chemical Changes
Changes in
chemical
composition;
NEW substance
MUST be present







Burning
Rusting
Formation of new gas
Formation of new solid
Change in pH
Growing new cells
Digestion
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Types of Evidence
LET’S
PRACTICE!
1. Make a T chart (with two headers) on your
paper. Physical Changes|Chemical Changes
2. Sort the cards into the two categories.
3. Let me check.
4. Copy the examples into your chart.
5. Practice with the worksheet.
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Work time!
1. Physical vs. Chemical Changes WS
2. Read/highlight back of WS,
“Differentiating class and individual
evidence”
3. Write a definition for class evidence and
for individual evidence in your notebook as
summary.
4. Work on witness experiment (plan, create
surveys, find video clips or pics, talk to
teachers, etc.)
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PHYSICAL EVIDENCE
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Warm up (Think, Pair, Share!):
If a forensic investigator has just the right
evidence, what are some specific facts the
evidence could prove? (For example, it can prove
that a crime was committed.)
List the following types of evidence in your
journal. What do you think each one means?
Share with your partner.
Transient evidence
Conditional evidence
Circumstantial evidence
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Types of Evidence
Physical Evidence
Is generally more reliable than testimonial
evidence
Can prove that a crime has been committed
Can corroborate or refute testimony
Can link a suspect with a victim or with a crime
scene
Can establish the identity of persons associated
with a crime
Can allow reconstruction of events of a crime
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Reconstruction
Physical evidence can be used to
answer questions about:
What took place at a crime scene
The number of people involved
The sequence of events
A forensic scientist compares the questioned or unknown
sample from the crime scene with a sample of known
origin.
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Types of Evidence
Transient evidence is temporary; easily changed
or lost; usually observed by the first officer at the
scene.
Odors such as perfume, putrification,
gasoline, cigarette smoke
Temperature of a coffee pot, car hood,
dead body, or water in bathtub
Imprints and indentations such as
footprints in sand, fingerprints in dust,
teeth marks in perishable foods
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Types of Evidence
Conditional evidence is produced by a
specific event or action; important in crime
scene reconstruction and in determining the
set of circumstances or sequence within a
particular event.
Lights on or off?
Garage door up or down?
Door open or closed?
Windows locked or unlocked?
Position of body or furniture?
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Circumstantial evidence implies a fact or event
without actually proving it.
More circumstantial evidence = more weight b/c
of probability and statistics
Ex: A blond hair is found in the hand of a murder victim
having black hair.
(circumstantial—lots of people have blond hair)
Size 11 sneaker print found near by
(circumstantial—lots of people have big feet)
Two observations together limit pool of suspects!
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Probability and Class Evidence Activity
Get out your calculator!
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Can I tell a Blonde joke?
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 The local police force was looking for a new detective, so a Blonde went
in to interview for the job. Okay, honey, the sheriff asked, “What is 1 and
1?” ” Eleven”, she replied. The sheriff thought to himself, that’s not what
I meant, but she’s right. Then the sheriff asked, “What two days of the
week start with the letter T?” “Today and tomorrow” she replied. He was
again surprised that the Blonde supplied a correct answer that he had
never thought of himself. “Now, listen carefully. Who killed Martin
Luther King?” Asked the sheriff. The Blonde thought really hard for a
minute and finally admitted she had no idea. The sheriff replied, “Well,
why don’t you go home and work on that one for a while?” So, the
Blonde left and went home. When she walked through the door her
husband asked her how the interview went. She replied , “It went great!
First day on the job and I’m already working on a murder case!”
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Other Evidence
Pattern evidence—mostly in the form of imprints, indentations,
striations, markings, fractures, or deposits
Blood spatter
Glass fracture
Fire burn pattern
Furniture position
Projectile trajectory
Tire marks or skid marks
Clothing or article
distribution
Gunpowder residue
Material damage
Body position
Toolmarks
Modus operandi
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Significance of Physical Evidence
Individual—can be identified with a particular
person or a single source
Blood DNA Typing
Fingerprints
Class—common to a group of objects or
persons
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Class vs. Individual Evidence
These fibers are class
evidence; there is no
way to determine if
they came from this
garment.
The large piece of glass
fits exactly to the bottle;
it is individual
evidence.
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Class vs. Individual Evidence, continued
Which examples do you think could be
individual evidence?
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Forensic Investigations
Include some or all of these seven major activities:
1. Recognition—the ability to distinguish important evidence
from unrelated material
Pattern recognition
Physical property observation
Information analysis
Field testing
2.
Preservation through the collection and proper packaging of
evidence
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Types of Evidence
Forensic Investigations, continued
3.
Identification using scientific testing
Physical properties
Chemical properties
Morphological (structural) properties
Biological properties
Immunological properties
4.
Comparison of class characteristics measured against those of
known standards or controls; if all measurements are equal, then
the two samples may be considered to have come from the same
source or origin
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Types of Evidence
Forensic Investigations, continued
5.
Individualization in demonstrating that the sample is unique, even
among members of the same class
6.
Interpretation—giving meaning to all the information
7.
Reconstruction of the events in the case
Inductive and deductive logic
Statistical data
Pattern analysis
Results of laboratory analysis
—Henry C. Lee and Jerry Labriola, Famous Crimes Revisited, 2001
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FBI Investigation
Read a case investigated by the FBI. Observe the various
units of their lab and read the section: “How Did They Do
That?”
www.fbi.gov/kids/6th12th/investigates/investigates.htm
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