Crime Scene Investigation Basics

Chapter 2: Evidence

• Edmund Locard (1877-1966)

  • Known for Locard's Exchange Principle: "every contact leaves a trace"
  • Explains how evidence is created and used to recreate an event
  • Established his forensic lab in 1910
  • Founded and directed the Institute of Criminology at the University of Lyon

• Evidence Types

  • Inclusive: Evidence that answers the question
  • Indeterminate: Evidence that doesn't help answer a question
  • Exclusive: Evidence that excludes a possibility, eliminating a possible answer to the question

• Forms of Evidence

  • Testimonial (eyewitness): Evidence recorded from a witness
  • Physical: Raw material examined by forensic scientists

Admissibility of Evidence

• Whether or not evidence can be used in court depends on the court's application of the rules of evidence

• Courts consider precedent when determining admissibility

• Courts ensure methods used for evidence are scientifically acceptable and reliable

• Court Standards

  • Frye Standard (Frye v. U.S.): Evidence must be generally acceptable to a significant portion of the scientific community
  • Federal Rules of Evidence & Daubert Standard: More flexible guidelines
  • 2016: 16% of states used Frye, 76% used Daubert, remaining states used other standards

• Categories of Evidence

  • Inculpatory or Exculpatory: Evidence that includes or excludes a person as a source
  • Direct or Circumstantial: Direct establishes information without further inference, while circumstantial serves as the basis for further inference. Most evidence is circumstantial

Methods of Interpretation

• 3 types:
  • Deductive: Similar to mathematical reasoning, drawing conclusions from facts.
  • Inductive: Uses existing data to make predictions and generalizations
  • Abductive: Most common, using known information to create the simplest and most likely explanation.

Chapter 3: Crime Scene Investigation

• Crime Scenes
  • Each scene is unique due to the chain of events, and they decay from the moment they are created
  • Forensic scientists analyze evidence to understand what happened during the criminal act, before and after.
  • Objective is to recognize, preserve, and collect physical evidence
  • Determining what is relevant is a primary challenge
• Types of Crime Scenes
  • Macroscopic: Crime scenes on a large scale
  • Secondary: Scenes created by acts following the original crime
  • Micro: Smaller parts of a scene, like a specific room

Initial Crime Scene Investigation

• First Responders: Complete initial work, ensuring safety
• CSI: Perform preliminary scene surveys/walk-throughs, taking photos and videos, noting special considerations (e.g., rain).
• Video recording and documentation are crucial

Crime Scene Documentation

• Types of Coordinate Systems
  • Triangulation: Points (X and Y) are fixed, evidence from X and Y measured, etc.
  • Polar Coordinates: Use measurements from a fixed point

Sketching the Crime Scene

• Important to accurately record measurements and perspective.
• Used for detailed analysis of locations, objects, and evidence.
• Forensic mapping and laser scanning are helpful (e.g., 3D mapping, Lidar, GPS).

Crime Scene Search Patterns

• No Pattern: Following the evidence
• Line/Strip: Used in large outdoor scenes
• Zone: Used in scenes with defined zones
• Wheel/Ray: Used in small, specialized scenes
• Spiral: Used in scenes without physical barriers

Evidence Management Flowcharts

• Documentation (marking the beginning of chain of custody procedures) details include date, collector, time, and a description of the objects.

Packing Evidence

• Different types require special container techniques
• Primary containers into secondary containers, with proper sealing and labeling
• Control samples should also be packaged and appropriately identified.

Chapter 5: Medico-Legal Investigation of Death

• Investigation of Death:

  • Questionable death (equivocal death) requires additional investigation when the cause is unclear.
  • Death investigation systems vary but usually involve legal officials and medical professionals.

• Death Scene Investigation

  • The primary focus is on the body and the scene, checking for post-mortem changes.

• Systems of Death Investigations

  • Coroner: Government agent with responsibility for death investigation
  • Medical Examiner: In some states, Medical Examiners (instead of Coroners) are licensed physicians with training and responsibilities.

• Time of Death: Estimate using knowledge of post-mortem changes.

Mechanism of Death

• Four main types (Natural, Accidental, Suicidal, Homicidal)

• Key changes after death include rigor mortis, livor mortis, and algor mortis (stiffening of body muscles, discoloration, and cooling, respectively).

Tools of Death Investigation

• Autopsies: Examination of the body (external and internal)
• Forensic pathology, including examination of organs
• Cause of death, manner of death
• Time of death, etc.

Crime Scene Investigation and Evidence

• Goal is to recognize, document, photograph, and collect evidence at a crime scene and secure it.
• Guidelines for evidence acceptability (must be reliable, consistent when tested, and valid) are used.

Types of Evidence

• Direct: First-hand observations like eyewitness or security footage
• Circumstantial: Indirect evidence implying facts but not directly proving them
• Physical & Biological Examples: Fingerprints, DNA, hair, bodily fluids, fibers. Trace evidence is also important.

Securing the Scene

• Safety and evidence preservation are priorities
• First responders keep a security log restricting unauthorized entry.

Scanning and Mapping the Scene

• Scanning: Establish which areas have been affected
• Mapping: Measuring distance.

Searching for Evidence

• Different patterns suit different crime scene configurations

  • ( e.g., Linear, Zone, Quadrant, Spiral )

• Evidence is documented

• Photos, sketches, labels of evidence are essential

Securing the Evidence

• Proper packaging is crucial
• Evidence storage must be labeled, sealed, and kept secure to maintain the chain of custody.

Mapping the Outdoor Crime Scene

• Establish a fixed reference point
• Record distance and angles from evidence to reference point
• Marked points on the scene (or collection site), for instance, north.
• This is used later for analysis.

Crime Scene Reconstruction

• Hypotheses using evidence to determine sequence of events.
• Guidelines help and establish criteria for evidence assessment.

Staged Crime Scenes

• Crime scenes manipulated which require additional investigation, to determine a plausible explanation.

Types of Crime Scene Sketches

• Rough sketches: Preliminary, less detailed sketches taken
• Finished sketches: Detailed sketches with measurements.

Chapter 12: Importance for Examining Death.

• Job of Coroner

• Identifying bodies; notifying families; collecting belongings

• Investigating suspicious deaths

• Systems Variety

  • Medical Examiners, etc.

• Manner/Cause of death

• Natural Death: Result from age, illness or exposure to harmful substances

• Accidental Death: Unplanned events like falls or accidents

• Suicidal Death: Deliberately taking one's own life

• Homicidal death: One person causing the death of another

• Undetermined: The cause of death can't be determined from an analysis of the body.

Process of Death

• Stage 1. Stoppage: Heart Stops, blood flow stops, etc

• Stage 2. Autolysis: Cell damage, cellular breakdown (enzymes).

• Characteristics of Death

  • Algor Mortis: Cooling of the body (temp loss after death)
  • Livor Mortis (Lividity): Discoloration of skin that occurs after a body stops moving

• Rigor Mortis: Stiffening of body muscles after death

• Decomposition Timeline: Decomposition occurs at different rates (environmental factors, body type).