Crime and Accident Reconstruction

Chapter 13 Crime and Accident Reconstruction

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.

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.

Introduction—Vocabulary

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

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

How Many Motives for a Murder?

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

Introduction

Reconstruction—the process of reproducing the actions and circumstances of an accident or crime based on examination and interpretation of evidence.

History (Obj 13.1)

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

Role of Evidence

Reconstructionists use evidence to:

•Establish a timeline of events and relationships

•Connect victims and suspects involved in the crime

Example: shoe tread

•Size

•Shape

•Pattern

•Depth

Crime-Scene Staging (Obj 13.2)

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:

•Suicide

•Accident

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

Reporting (Obj 13.4)

Level One

Collecting basic information

•Facts

•No opinions

At-The-Scene Investigation (Obj 13.4, 13.5)

Level Two

Photographs and Measurements

Coefficient of Friction

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

Examinations

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

Technical Follow-Up (Obj 13.4)

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

Accident Reconstruction (Obj 13.4, 13.6)

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

Law of Conservation of Momentum

Work (w)—the amount of energy transferred by a force (F) acting through a distance (d).

w = F x d

Newton’s Laws of Motion

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

Newton’s Laws of Motion

Second Law—expresses the relationships among acceleration (a), force (f), mass (m)

Third Law—for every action, there is an equal and opposite reaction

Law of Conservation of Momentum (Obj 13.6)

Momentum (p) = Mass (m) x Velocity (v)

p = m x v

Cause Analysis (Obj 13.4)

Level Five

Experts share in court, based on facts and research, how and why an accident occurred

Conflicting analyses are possible

Pitfalls of Reconstruction

Chapter Summary

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.

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.

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

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