Tuesday 11/13/12
• AIM: How does physical evidence
collected at a crime scene help to solve
the case?
• DO NOW: 1- Define Physical evidence
• 2-List at least 5 types of physical evidence
found at a crime scene.
• Homework: Take home exam Chapter 2
Physical evidence
• Any solid or tangible piece of evidence
that is collected at a crime scene and:
– Tells us that a crime has been committed
– connects a crime to a suspect and/or victim
• Handout. Thumb tips off cops
• Read to yourself and answer questions on
the back.
Physical Evidence
• “This is evidence that does not forget.
It is not confused by the excitement of
the moment. It is not absent because
human witnesses are, it is factual
evidence, physical evidence cannot be
wrong, it cannot perjure itself… only its
interpretation can err.”
- Paul L. Kirk, 1974
• 1. Blood, semen, and saliva. These
substances are subjected to
serological and biochemical analysis
for determination of identity and
possible origin.
Semen: water, sugar, sperm
Wednesday11/14/12
• AIM: What are the different types of
physical evidence collected from a crime
scene?
• DO NOW: take out a # 2 pencil and your
take home test
• Fill in your scantron
• HOMEWORK: textbook Read pages 6264. choose any 5 types of physical
evidence to list and describe
Saliva
• Water, enzymes, epithelial cells
• Epithelial cells: source of DNA
• 2. Documents. Any handwriting and
typewriting examined for authenticity
or source.
• 3. Drugs. Any substances seized in
violation of laws regulating the sale,
manufacture, distribution, and use of
drugs.
• 4. Explosives. Any device containing
an explosive charge, as well as all
objects removed from the scene of an
explosion that are suspected to
contain the residues of an explosive.
• 5.
Fingerprints.
All prints of
this nature,
latent and
visible.
• 6. Fibers. Any natural or synthetic
fiber whose transfer may be useful in
establishing a relationship between
objects and/or persons.
• 7. Firearms and
ammunition. Any
firearm, as well
as discharged or
intact
ammunition,
suspected of
being involved in
a criminal
offense.
Period 3 Friday 11/16/12
Aim: How can we distinguish
individual and class characteristics?
Do Now:What is the source of DNA
in each of the following: Blood,
semen, saliva
HOMEWORK: Textbook read pages 6566. Answer questions 1-5 pages 74-75
• Textbook read pages 36-41. answer
questions 1-3 on page 46
Physical Evidence
• Forensic scientist: determine the identity and
origin of physical evidence
• Physical properties: color,
density,solubility,refractive index
– EASILY MEASURED
• Chemical properties: observed when there is a
reaction with another chemical
–
–
–
–
Bubble formation( liquid to gas phase change)
pH (percent hydrogen)
Color change
Precipitate formation
Case Study: Coral Eugene Watts
•
•
•
•
Texas and Michigan
Burglary and intent to murder
1982 conviction
Testimonial evidence: Watts confessed to killing
13 woman but he was tried for 1
• Lack of physical evidence
• He stated he was responsible for 20 other
murders
• Modus Operandi was different in each murder
(unlikely for a serial killer)
Coral Watts continued
• Final conviction was based on the
testimonial evidence of Joseph Foy in the
murder of Helen Dutcher
• Michigan 1979.
• Eyewitness account 25 years prior which
was the only evidence admitted
• At his trial he confessed to 80 other
murders
Individual vs class evidence
• Individual Evidence:
can be linked to one
single person
• Class evidence:
linked to a group of
people
How can we individualize the
following pieces of evidence?
• 1- A medium, Gap, white T-shirt
– Gets torn at a crime scene
• 8. Glass. Fragments may be
transferred to a person or object
during a crime.
• 9. Hair. Collected hairs can link a
person to a crime.
• 10. Impressions. This category
includes tire markings, shoe prints,
bite marks in skin or food
• Trace evidence: Any small item
of evidence – hair, fiber, paint,
glass, or soil, for example – that
places the suspect at the scene
of the crime or in direct contact
with the victim is considered
trace evidence.
Pd 5 Friday 11/16/12
• AIM: How can we analyze physical evidence
extracted from a crime scene?
• DO NOW: Classify each of the following as
individual or class evidence. Explain how you
would individualize each piece of class
evidence.
• 1- A bloody knife found in the backyard of a
murder suspect
• 2- A tire impression from a 1993 honda Civic
• 3- A cigarette butt found at a crime scene
• 4- A paint chip with five layers of paint
Product Rule
• Used in attempt to individualize class
evidence
• Multiply the frequency of independent
genetic markers to obtain the overall
frequency of occurrence
• Help create an individual genetic profile
Collecting Evidence At A Crime
Scene (At The Scene Of A Crime)
Assessment
• What type of physical
evidence would you
collect from the crime
scene to your right?
• For each piece of
evidence explain if it
is individual or class
• AIM: how can we collect physical evidence
from a crime scene?
• DO NOW: 1906 NYPD fingerprinting
handout.
• Homework: Textbook read pages 70-73.
answer questions 1-13 pgs 74-75.
• AIM: What are some types of physical evidence
collected at a crime scene?
• DO NOW: analysis of paint chips and hair fibers
handout
• Homework; Textbook read pages 63-66. List
and describe the significance of physical
evidence at a crime scene
• Textbook read pages 67-70. If you were a juror
and the suspect has blood type A but only blood
types AB and O are found at the crime scene,
would you convict him/her?