In-depth Notes on Crime Scene Investigation

Crime Scene Investigation Principles

Associative Evidence

• Definition: Links individuals to the crime scene.
• Significance: First crucial step in forensic sciences, necessary for court presentation and further analysis.
• Skills Required:
• Documenting
• Preserving evidence
• Methods of Documentation:
• Photographs: Visual records of the crime scene.
• Sketches: Diagrammatic representations indicating evidence locations.
• Collecting Physical Evidence: Gathering tangible items relevant to the crime.
• Purpose: Helps determine the cause of death, individuals involved, and the sequence of events.
• Locard’s Exchange Principle: "Every contact leaves a trace."
• Origin: Created by Dr. Edmond Locard, known as the "Sherlock Holmes of France."
• Example: A burglar takes traces from a home while leaving their traces behind.
• Types of Associative Evidence:
• Fingerprints
• Blood/Bodily fluids
• Hair/Fibers
• Weapons

Gauging the Value of Evidence

• Importance of understanding when a crime scene investigation is conducted:
• Cases Involving: Burglaries, violent crimes, suicides, fires, auto thefts, accidents.
• Types of Evidence: Determined by case circumstances; gathering physical evidence helps recreate crime events and validate claims.

Reconstructive and Circumstantial Evidence

• Reconstructive Evidence: Answers questions about what happened.
• Examples: Broken windows, blood patterns, bullet paths, shoe prints.
• Circumstantial Evidence: Indirect evidence requiring inference. Can include:
• Eyewitness observations (not admissible alone in court).
• Samples that indirectly suggest involvement (e.g., glass shards on a suspect).

Uniqueness of Evidence

• Unique evidence increases the likelihood of identifying a suspect.
• Examples: Shoe prints and tire imprints.
• Probability Consideration:
• Low Probability: Evidence unlikely to occur by chance is more compelling.
• High Probability: Common types of evidence still serve a role in narrowing a suspect pool.
• Inconsistency Consideration: Elements that are out of character or inconsistent can be significant evidence (e.g., a non-smoker with a cigarette at the crime scene).

Crime Scene Investigation Process

• Investigators must gather and analyze evidence from both primary and secondary scenes.
• Physical Evidence Types:
• Probative Evidence: Evidence that can prove something.
  • Biological (e.g., blood, body fluids)
  • Latent prints (e.g., fingerprints, palm prints)
  • Trace evidence (fibers, soil)
  • Digital evidence (cell phone records, email logs)

Crime Scene Team and Roles

• Detective: Leads the investigation; interviews witnesses; builds a case.
• Crime Scene Investigator: Processes the scene; documents, collects, and secures evidence.
• Forensic Pathologist: Determines cause of death through autopsies.
• Forensic Odontologist: Identifies remains and bite marks.
• Forensic Toxicologist: Analyzes bodily fluids for substances.
• Forensic Anthropologist: Identifies skeletal remains and estimates time of death.
• Forensic Biologist: Analyzes biological samples for DNA.
• Forensic Chemist: Analyzes physical evidence for chemicals.
• Fingerprint Analyst: Matches fingerprints found at crime scenes.
• Digital Forensics Specialist: Recovers data from electronic devices.
• Crime Scene Photographer: Documents visual evidence for court.

Chain of Custody

• Definition: Tracking evidence from collection to court presentation to ensure integrity.
• Steps in Chain of Custody:

1. Collection: Document who collected, when, and where.
2. Labeling/Packaging: Properly label and package to prevent contamination.
3. Transport: Secure transportation with logs of handlers.
4. Storage: Secure storage with limited access.
5. Documentation: Detailed logs of evidence handling.
6. Court Presentation: Must include chain of custody for evidence validity.

• Challenges: A break in the chain can lead to evidence being inadmissible.

Forensic Lab Techniques

DNA Analysis & Profiling

• Techniques:
• Polymerase Chain Reaction (PCR): Amplifies DNA for analysis.
• Short Tandem Repeats (STR): Unique markers in DNA for identification.

Forensic Toxicology

• Techniques:
• Gas Chromatography-Mass Spectrometry (GC-MS): Reliable substance detection.
• Immunoassay: Rapid tests for drugs/toxins.

Ballistics Analysis

• Techniques:
• Comparison Microscopy: Links bullets to firearms.
• Gunshot Residue Testing: Detects particles from firearm discharge.

Blood Spatter Analysis

• Study of Patterns: Determines position and movements during events.

Fiber & Trace Evidence

• Microscopy: Compares fibers from crime scenes to suspects.