Transcript FSII ch13 presentation

Chapter 13
Crime and
Accident
Reconstruction
© 2012 Cengage Learning. All Rights Reserved
Introduction—Objectives
1. Discuss the contributions of various forensic
specialists to crime reconstruction.
2. Discuss possible motives for crime-scene
staging.
3. Discuss the factors involved in a motor
vehicle collision.
4. Describe the five levels of an accident
investigation.
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Forensic Science II: Crime and Accident Reconstruction, Chapter 13
© 2012 Cengage Learning. All Rights Reserved
Introduction—Objectives
5. Compare and contrast skid marks and yaw
marks.
6. Explain the importance of the law of
conservation of momentum and law of
conservation of energy in accident
reconstruction.
7. Evaluate factors that can lead to incorrect
reconstruction.
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Forensic Science II: Crime and Accident Reconstruction, Chapter 13
© 2012 Cengage Learning. All Rights Reserved
Introduction—Vocabulary
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contact damage—damage to a vehicle caused by
contact with an object or other vehicle
law of conservation of energy—rule that states
that energy is neither created nor destroyed, but it
can be converted into different forms
law of conservation of momentum—rule that
states that the momentum of a system remains
unchanged unless a force acts upon it
Forensic Science II: Crime and Accident Reconstruction, Chapter 13
© 2012 Cengage Learning. All Rights Reserved
Introduction—Vocabulary
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reconstruction—in criminal investigations, the
process of recreating the actions and circumstances
based on examination and interpretation of evidence
skid marks—marks left on the roadway by the tires
when the driver of the vehicle applies the brakes
suddenly
staging—the intentional altering of a crime scene in
order to disguise what really happened
yaw marks—skid marks in a curved path as a result
of an out-of-control skid
Forensic Science II: Crime and Accident Reconstruction, Chapter 13
© 2012 Cengage Learning. All Rights Reserved
How Many Motives for a Murder?
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July 4, 1954 Marilyn Sheppard was murdered
in her bedroom
Husband, Samuel, became the chief suspect
after knowledge of an affair became known
Samuel was tried and convicted of murder
On appeal, Dr. Kirk reconstructed the crime
scene to prove that a third person was there
Conviction overturned
Forensic Science II: Crime and Accident Reconstruction, Chapter 13
© 2012 Cengage Learning. All Rights Reserved
Introduction
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Reconstruction—the process of
reproducing the actions and circumstances
of an accident or crime based on
examination and interpretation of evidence.
Forensic Science II: Crime and Accident Reconstruction, Chapter 13
© 2012 Cengage Learning. All Rights Reserved
History (Obj 13.1)
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Dr. Hans Gross—authored textbook on systematic
methods for analyzing facts of a criminal case
Dr. Alexandre Lacassagne—advocated
combining science with criminology
Dr. Edmond Locard—exchange principle
Edward Heinrich—forensics requires broad
knowledge in many fields of science
Dr. Paul Kirk—a dissertation described principles of
crime reconstruction
Forensic Science II: Crime and Accident Reconstruction, Chapter 13
© 2012 Cengage Learning. All Rights Reserved
Role of Evidence
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Reconstructionists use evidence to:
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Example: shoe tread
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Establish a timeline of events and relationships
Connect victims and suspects involved in the
crime
Size
Shape
Pattern
Depth
Forensic Science II: Crime and Accident Reconstruction, Chapter 13
© 2012 Cengage Learning. All Rights Reserved
Crime-Scene Staging (Obj 13.2)
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Reconstructionists must be aware that
crimes may have been staged
Staging—the intentional altering of a crime
scene in order to disguise what really
happened.
Making crimes appear to be:
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Suicide
Accident
Forensic Science II: Crime and Accident Reconstruction, Chapter 13
© 2012 Cengage Learning. All Rights Reserved
Accident Investigation (Obj 13.3)
Level 1: Reporting
Level 2: At-the-scene investigation
Level 3: Technical follow-up
Level 4: Accident reconstruction
Level 5: Cause analysis
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Forensic Science II: Crime and Accident Reconstruction, Chapter 13
© 2012 Cengage Learning. All Rights Reserved
Reporting (Obj 13.4)
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Level One
Collecting basic
information
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Facts
No opinions
Forensic Science II: Crime and Accident Reconstruction, Chapter 13
© 2012 Cengage Learning. All Rights Reserved
At-The-Scene Investigation (Obj 13.4, 13.5)
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Level Two
Photographs and Measurements
Forensic Science II: Crime and Accident Reconstruction, Chapter 13
© 2012 Cengage Learning. All Rights Reserved
Coefficient of Friction
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Coefficient of Friction—a quantitative
value, determined through experimentation
that measures the roughness of a surface.
s2 = 255df
s = speed of travel (km/h)
d = distance (length) of skid mark
f = coefficient of friction
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Forensic Science II: Crime and Accident Reconstruction, Chapter 13
© 2012 Cengage Learning. All Rights Reserved
Coefficient of Friction
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Forensic Science II: Crime and Accident Reconstruction, Chapter 13
© 2012 Cengage Learning. All Rights Reserved
Examinations
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Was alcohol a factor?
Contact damage—damage on a vehicle
made by another object or vehicle
Equipment failure
Occupant restraints
Maintenance of tires, air pressure,
headlights, taillights
Forensic Science II: Crime and Accident Reconstruction, Chapter 13
© 2012 Cengage Learning. All Rights Reserved
Technical Follow-Up (Obj 13.4)
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Level Three
Used when a crime has been committed
Prepare a map of the crime site
Interview witnesses
Assess visibility at the site
Evaluate evidence (e.g., paint chips)
Toxicology report
Autopsy report when there’s a fatality
Forensic Science II: Crime and Accident Reconstruction, Chapter 13
© 2012 Cengage Learning. All Rights Reserved
Accident Reconstruction (Obj 13.4, 13.6)
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Level Four
Law of conservation of momentum
—rule that states that the momentum of a
system remains unchanged unless a force
acts upon it
—energy cannot be created or destroyed,
but can be converted from one form to
another
Forensic Science II: Crime and Accident Reconstruction, Chapter 13
© 2012 Cengage Learning. All Rights Reserved
Law of
Conservation of Momentum
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Work (w)—the amount of energy transferred
by a force (F) acting through a distance (d).
w=Fxd
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Forensic Science II: Crime and Accident Reconstruction, Chapter 13
© 2012 Cengage Learning. All Rights Reserved
Newton’s Laws of Motion
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First Law—Law of Inertia
a) an object at rest will remain at rest, and
b) an object in motion will remain in motion
with a constant velocity unless some external
force acts on the object
Forensic Science II: Crime and Accident Reconstruction, Chapter 13
© 2012 Cengage Learning. All Rights Reserved
Newton’s Laws of Motion
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Second Law—expresses the relationships
among acceleration (a), force (f), mass (m)
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Third Law—for every action, there is an
equal and opposite reaction
Forensic Science II: Crime and Accident Reconstruction, Chapter 13
© 2012 Cengage Learning. All Rights Reserved
Law of
Conservation of Momentum (Obj 13.6)
Momentum (p) = Mass (m) x Velocity (v)
p=mxv
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Forensic Science II: Crime and Accident Reconstruction, Chapter 13
© 2012 Cengage Learning. All Rights Reserved
Cause Analysis (Obj 13.4)
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Level Five
Experts share in court, based on facts and
research, how and why an accident occurred
Conflicting analyses are possible
Forensic Science II: Crime and Accident Reconstruction, Chapter 13
© 2012 Cengage Learning. All Rights Reserved
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Forensic Science II: Crime and Accident Reconstruction, Chapter 13
© 2012 Cengage Learning. All Rights Reserved
Pitfalls of Reconstruction
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Forensic Science II: Crime and Accident Reconstruction, Chapter 13
© 2012 Cengage Learning. All Rights Reserved
Chapter Summary
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Several forensic investigators contributed to the
acceptance of crime reconstruction as a scientific,
logical, and objective process.
Evidence helps crime reconstructionists establish a
sequence of events leading up to the crime as well
as relationships between the scene, the victim, and
the suspect.
Forensic investigators and scientists rely on analysis
of evidence as well as witness accounts to recreate
or reconstruct a chain of events.
Forensic Science II: Crime and Accident Reconstruction, Chapter 13
© 2012 Cengage Learning. All Rights Reserved
Chapter Summary
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Staged crime scenes are usually an attempt to cover
up a murder or insurance fraud.
All accidents must be reported at level one, but
accidents that require research and potential
litigation require all five levels of investigation.
Skid marks and yaw marks help investigators
determine the speed at which a vehicle was traveling
prior to a collision or accident.
Forensic Science II: Crime and Accident Reconstruction, Chapter 13
© 2012 Cengage Learning. All Rights Reserved
Chapter Summary
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Investigators use the law of conservation of
momentum and the law of conservation of energy to
determine initial velocity of the collided vehicles.
The three main causes of accidents are:
• Environmental factors
• Human factors
• Vehicular malfunction
To ensure the validity of reconstruction
• avoid flaws in logic
Forensic Science II: Crime and Accident Reconstruction, Chapter 13
© 2012 Cengage Learning. All Rights Reserved