Ch 3 Evidence
Forensic Science
9/15/15
Drill
• New seats!
• Pick up notes packet – four sheets
• Take out a sheet of notebook paper.
• Number it #1-5
Drill – Homework Review
1. Was the killer in the Green River killings:
A.Gary Ridgway
B.Thomas Hardy
C.Kyle Carter
D.Hannibal Lecter
Drill – Homework Review
2. Most of the victims of the Green River killer
were:
A.
B.
C.
D.
College students
Children
Prostitutes
Dancers
Drill – Homework Review
3. True or False? The perpetrator of the crimes
passed a lie detector test about the crimes.
Drill – Homework Review
4. The DNA evidence that tied the accused to
the crime was from comparing:
A.
B.
C.
D.
skin and blood
blood and hair
hair and saliva
saliva and semen
Drill – Homework Review
5. Minute amounts of
were found
on the clothing of the victims and in the
murderer’s workplace.
A.
B.
C.
D.
ash
paint
resin
pollen
Now, to grade!
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Trade with someone near you.
Grade out of 5 points.
We’re hoping for 4/5 or better!
Write “Graded by (your name)” on the paper.
Answers
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1. A
2. C
3. True
4. D
5. B
Objectives
• SWBAT
• Name many forms of physical evidence.
• Classify evidence as indirect (circumstantial) or
direct.
• Classify evidence as individual or class.
Types of Evidence
Types of Evidence
• Evidence can be divided into two types of
evidence
• Direct evidence – evidence in the form of a
statement made under oath, such as a witness
pointing to a person in a court saying “that’s the
guy who robbed the grocery store.”
• Also known as testimonial evidence.
Types of Evidence
• Evidence can be divided into two types of
evidence
• Physical evidence – any object or material that is
relevant in a crime (also called trace evidence)
• Almost any tangible thing, as large as a plane, as
small as hair, as fleeting as an odor, or as obvious
as a demolished building.
Locard’s principle
• Edmond Locard, a French Forensic Scientitst:
• Always an exchange or transfer of material
when two objects came into contact.
Types of Common Physical Evidence
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Drugs and toxic substances
Paints
Gunshot residues
Firearms and ammunition
Impressions (shoes, teeth)
Petroleum products
Alcohols (especially ethanol)
Rubber material
Resins, plastics
Explosive residues
Serial numbers
documents
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fibers,
Soil, glass
Blood
body fluids
Fingerprints
Hair
Tissues
Pollen
Wood material
Feathers
bones
Types of Evidence
• Most evidence does not prove a fact and is
termed indirect or circumstantial evidence.
• Some physical evidence, however, may be
considered proof of fact, such as possessing a
controlled substance or a driver’s blood alcohol
level of greater than 0.08%.
Types of Evidence
• Circumstantial evidence – implies a fact or
event. The greater volume of circumstantial
evidence there is, the greater the weight it
carries. Probability and statistics come into
play here.
Types of Evidence
Explain why this would be or
would not be trace evidence
Forensic Science: Fundamentals & Investigations, Chapter
18 2
So, What Good is Evidence?
• Physical evidence can
• Prove that a crime has been committed
• Corroborate testimony
• Link a suspect with a victim or with a crime
scene
• Establish the identity of persons associated with a
crime
• Allow reconstruction of events of a crime
Rules of Evidence
• Define what evidence is acceptable
(admissible) and how it can be used for the
jury.
• Evidence must be relevant, meaning it must
prove something (probative) and address the
issue of the particular crime (material).
Rules of Evidence
• Evidence is admissible if it is reliable and the
presenter of such evidence is credible and
competent.
• Generally, hearsay is inadmissible in criminal
court because it is not reliable nor was it
taken under oath and therefore does not allow
for cross-examination. Hearsay is admissible
in civil suits.
Two legal decisions
• Legal decisions that govern the admissibility
of scientific evidence:
• Frye versus United States, 1923
• Daubert versus Merrell Dow Pharmaceutical,
Inc.
Frye Standard
• Interpretation of scientific evidence must be given
by an expert witness and have gained “general
acceptance” in the particular field of study.
• The court must decide if the questioned procedure,
technique, and principles are generally accepted by a
meaningful segment of the relevant scientific
community.
• Does not offer guidance on reliability.
Daubert ruling
• Trial judge must assume responsibility and validity
of evidence presented in their court. Guidelines:
• The scientific theory or technique must be testable.
• The theory or technique must be subject to peer review
and publication.
• Rate of error or potential errors must be stated.
• The technique must follow standards.
• Consideration must be given as to whether the theory or
technique has attracted widespread acceptance within a
relevant scientific community.
Individual versus Class Evidence
• Individual – best evidence, can be to a single
specific source, so there is no doubt as to what the
source of the evidence is.
• Type of evidence can place a suspect at a crime scene,
associate a suspect with a victim, and sometimes even
prove who committed the crime.
• Human characteristics that can be linked to an individual
are fingerprints, DNA analysis, handwriting, voice prints.
• Individualization always involves comparison.
Individual versus Class Evidence
• Class evidence is evidence found to be consistent
with a particular source.
• Class evidence alone may or may not be very
convincing in a crime, but if there are many different
types or pieces of class evidence, the value can be
considerable.
• Class evidence is associated with a group or class,
like polyester or blue polyester shirts.
• Examples of class evidence are hair, fibers, soil, and
glass fragments.
Individual vs. Class Characteristics
• Any item can have both individual and class
characteristics.
• What do I mean?
• ex. Roll of tape, earbuds, pencil
• Look at your shoe—make a list of
• class characteristics
• individual characteristics
For example
• Pens – who has a…
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pen
ballpoint
black ink
Bic brand
Howard Community College
broken pocket clip
• Which are class? Which are individual?
Individual
Characteristics
Class
Characteristics
Purpose of Examining Physical
Evidence
• The examination of physical evidence by a
forensic scientist is usually undertaken for
identification or comparison purposes.
Identification
• The purpose of
identification is to
determine the physical or
chemical identity of a
substance with as near
absolute certainty as
existing analytical
techniques will permit.
• In other words, WHAT IS
IT???
• Red stain: paint or blood?
Comparison
• In a comparison analysis,
a standard/reference
sample and the suspect
sample are given the
same tests and are
examined in the same
way.
• This is to determine if
they came from the same
place.
Example
• What are these?
(Identification)
• Fingerprints
• Whose are they?
(Comparison)
• If you don’t have
anything to compare to,
you can’t do anything
else!
Identification
• First, test procedures must be developed that give
the same results every time, for standard materials.
• Next, the same procedures must be used every time
to prove the identity of suspect materials.
• Finally, there need to be enough tests so that no
other material could give the same results.
• Example – Ms. Bloedorn’s “-caine” experience
Common Types of Identification
• The crime laboratory is
frequently requested to
identify the chemical
composition of an illicit
drug.
• It may be asked to
identify gasoline in
residues recovered
from the debris of a
fire, or it may have to
identify the nature of
explosive residues—for
example, dynamite or
TNT.
• The
identification of
blood, semen,
hair, or wood are
also very
common and, as
a matter of
routine, include
a determination
for species
origin.
Comparison
• A comparative analysis has the important role of
determining whether or not a suspect specimen and a
standard/reference specimen have a common origin.
• Both the standard/reference and the suspect
specimen are subject to the same tests.
• The forensic comparison is
actually a two-step
procedure.
• First, combinations of select
properties are chosen from
the suspect and the
standard/reference specimen
for comparison.
• Second, once the
examination has been
completed, the forensic
scientist must be prepared to
give a conclusion with
respect to the origins.
Natural vs. Evidential Limits
• There are practical limits to the properties and
characteristics the forensic scientist can select for
comparison.
• Modern analytical techniques have become so
sophisticated and sensitive that natural variations in
objects become almost infinite.
• Example: Electron micrograph of paper
No two pieces of paper will be the
same at this magnification.
What good is class evidence?
• The product rule is a formula for
determining how frequently a certain
combination of characteristics occurs in a
population.
• Product Rule Example & WS
Forensic Databases
There are four databases you need to
know about.
IAFIS
• The Integrated Automated
Fingerprint Identification
System (IAFIS), a national
fingerprint and criminal
history system maintained
by the FBI.
CODIS
• The Combined DNA Index
System (CODIS) enables
federal, state, and local
crime laboratories to
electronically exchange and
compare DNA profiles.
NIBIN
• The National Integrated
Ballistics Information
Network (NIBIN) allows
firearm analysts to acquire,
digitize, and compare
markings made by a
firearm on bullets and
cartridge casings.
PDQ & SICAR
• The International Forensic
Automotive Paint Data
Query (PDQ) database
contains chemical and color
information pertaining to
original automotive paints.
• SICAR (shoeprint image
capture and retrieval) is a
shoeprint database.
Closure
• Choose an object.
• List the individual and class evidence about
that object.
• Is there any evidence (fingerprints?) that
could be identified? Compared?