Crime Scene - Forensic Science - Lecture Slides, Slides of Forensics

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The Crime Scene

Chapter 2

Physical Evidence

• Any and all objects that can establish that a crime has been committed or can provide a link between a crime and its victim or a crime and its perpetrator.
• The recognition of physical evidence is essential to the success of the crime lab.
• Types
  • Direct
    • first-hand observations, confessions, video
  • Circumstantial
    • Indirect evidence can imply a fact but not prove it – Suspects fingerprints at the scene

Classification of Evidence

Evidence

Circumstantial

Class

Individual Direct

• No amount of expensive, sophisticated lab equipment can salvage the investigation if physical evidence is not recognized and correctly collected and preserved.
• In reality only crimes of a serious nature will require evidence collection

Securing the Crime Scene

• Anyone who enters the crime scene can alter or change the scene and its evidence
• Access should be limited to crime scene personal and a contamination log should be kept.
• Witnesses are separated to prevent collusion.
• Must be guarded 24hrs a day until released
• A walk-through should be completed

Walkthrough

• Preliminary scene survey
• Mentally reconstruct the crime (this can be changed or adapted)
• Determine the boundaries
• Note any temporary evidence that requires immediate processing or protection
• Make a note of weather conditions and take precautions if necessary

Notes

• Must include a detailed written description of the scene with the locations of where physical evidence was recovered
• Must identify the time physical evidence was recovered, by whom, how, and by whom it was packaged and marked
• Tape-recording and narrating a video tape can be faster than writing.
• At some points notes must be transcribed

Videography

• Done without verbal commentary except for factual info such as date and time
• Should include both general and specific areas
• View of the crime scene from the victim’s point of view

Diagram

• Make a diagram or sketch that shows the spatial relationships that a photograph cannot

Search for Evidence

• Depends on the location of the crime
• Evidence searched for depends on the nature of the crime
• Important to note what is missing as well

Theories behind searches

• The Linkage Theory
  • The theory that if investigators can establish positive links between evidence, the crime scene, and the suspect then the case may be solved
  • Ex: Bloody fingerprints on the victim’s wrist and on the door knob would be useful while bloody fingerprints on only the doorknob would be less useful.

Theories behind searches

• Locard’s Theory of Exchange
  • Transfer evidence is created whenever two objects come into contact with each other. - Primary transfer---victim bleeding onto floor - Secondary transfer---suspect steps in blood on the floor and tracks it through the crime scene

Search Methods

• Line
  • Lots of people walk side by side across some large area like a field. - Very easy and works well in outdoor areas - Can be modified into the strip method by dividing the area into a rectangle which is then divided into strips

Search Methods

• Grid
  • After the line method has been used the area is searched perpendicular to the original area so that if the searches were over laid they would form a grid
  • Benefit is that two different people search the same area