Introduction to Forensic Science and Physical Evidence

Note-Taking Procedures and Class Requirements

• Paper Notes Requirement: Notes should be organized and written on paper.

• Submission Details: Notes are submitted at the conclusion of each lecture for a total of $10\text{ points}$.

• Lecture Priorities:

  • Active listening and active participation take precedence over raw note writing.

  • Notes should not be a word-for-word copy of presented material to prevent wrist strain.

  • Reference slides are permanently accessible on Canvas.

Introduction and History of Forensic Science

• Etymology of Forensics: The term "forensics" derives from the Latin phrase meaning "of the Forum."

• Core Definition: Forensic science is the application of scientific principles to investigate crimes and process physical or digital evidence.

• Pioneer of Forensic Science:

  • Edmond Locard: Recognized as the first proper forensic scientist.

  • Historical Milestone (1910): In 1910, Edmond Locard requested and established a formal scientific laboratory in the attic of a police station in France.

  • Locard's Exchange Principle: Formulated by Edmond Locard, this foundational principle of forensic science dictates: "every contact leaves a trace."

Categories of Physical Evidence

Physical evidence is grouped into four primary functional categories:

• Inceptive Evidence:

  • Definition: Evidence that initiates an investigation by indicating or suggesting that a crime was actually committed rather than an accidental occurrence.

  • Context and Examples: A burning house alone does not automatically demonstrate criminal intent; however, finding an accelerant gas can and matches at the scene serves as inceptive evidence that triggers an official criminal investigation.

• Identifying Evidence:

  • Definition: Evidence capable of identifying that a specific individual or specific object was present at the scene of a crime.

  • Context and Examples:

  • Personal Identification: Fingerprints and DNA profiles explicitly verify whether a victim or suspect was physically present at the scene.

  • Object Identification: A recovered bullet from a crime scene indicates the specific type of firearm utilized or matches the exact unique gun fired.

• Associative Evidence:

  • Definition: Evidence that connects or associates a crime with a specific person, place, or object, without definitively confirming that the person was physically present during the actual commission of the crime.

  • Context and Examples: If a murder occurs at a workplace while an individual is the sole working employee on site, that circumstance acts as associative evidence linking the employee to the crime, regardless of actual guilt or innocence.

• Corroborative Evidence:

  • Definition: Evidence that supports, confirms, or strengthens connections established by other pieces of evidence, statements, or accusations.

  • Context and Examples: Corroborative evidence is frequently utilized to validate witness statements or victim accusations. For instance, if an eyewitness reports seeing a green car strike another vehicle at an intersection, the discovery of a small streak of green paint on the victim's damaged vehicle corroborates the eyewitness claim.

Crime Scene Analysis Case Studies

• Case Study 1: Jewelry Store Burglary

  • Scenario Overview: A jewelry store is broken into overnight. The front glass door is shattered, and multiple jewelry items are stolen from a display case. Investigators locate a partial fingerprint on the display case and a torn piece of fabric snagged on the broken glass. Security video captures blurry footage of a figure breaking in. Later, police stop a suspect possessing a cut on his hand and wearing a damaged jacket.

  • Evidence Classifications:

  • Inceptive Evidence: The shattered glass door (establishes the entry point/break-in) and missing jewelry (establishes that a burglary occurred).

  • Identifying Evidence: The partial fingerprint found on the display case (identifies the specific suspect).

  • Associative Evidence: The torn piece of fabric snagged on broken glass (links the suspect's attire to the physical crime scene).

  • Corroborative Evidence: The security camera footage (supports overall evidence by demonstrating the break-in) and the suspect's hand injury and damaged jacket (corroborate the fabric snag and break-in event with the specific suspect).

• Case Study 2: Hit-and-Run Vehicle Collision

  • Scenario Overview: A pedestrian is struck by a motor vehicle on a rainy evening, and the vehicle flees the scene. At the impact site, officers find skid marks and a broken headlight fragment. Eyewitnesses report a dark-colored sedan driving away rapidly. Traces of paint matching a suspect's vehicle are discovered on the victim's clothing, and cellular phone records place the suspect in the immediate vicinity at the exact time of the collision.

  • Evidence Classifications:

  • Inceptive Evidence: Skid marks (demonstrate where the incident originated) and the injured victim (indicates an accident or violent event occurred).

  • Identifying Evidence: The broken headlight fragment (serves to identify the specific vehicle make, model, or individual suspect vehicle).

  • Associative Evidence: Paint traces left on the victim's clothing (connects the victim directly to the vehicle) and mobile phone records (verifies the suspect's geographic presence near the scene).

  • Corroborative Evidence: Eyewitness accounts describing a dark-colored sedan (corroborate the vehicle paint evidence and physical headlight remnants).

Evidence Classification Characteristics

Forensic evidence is further distinguished by the precision of its source attribution:

• Individual Characteristics:

  • Definition: Properties of evidence that can be attributed to a single, specific source or individual with an extremely high degree of certainty.

  • Examples: Fingerprints, DNA evidence, and unique tool marks (such as individual hammer strike impressions).

  • Significance: Crucial for establishing conclusive links between an exact suspect or tool and a crime scene.

• Class Characteristics:

  • Definition: Properties of evidence that can be associated only with a group, category, or collective source, rather than a single individual entity.

  • Examples: ABO blood typing, tire tread designs, general bullet shell casing styles, and factory paint chips.

  • Significance: Essential to collect and analyze because they eliminate non-matching sources, narrow down pools of potential suspects or objects, and corroborate other evidentiary links.

Legal Admissibility of Evidence

For physical evidence to be presented effectively within a court of law, strict legal standards must be satisfied:

• Inadmissible Evidence:

  • Definition: Evidence that cannot be legally introduced or presented in court proceedings, regardless of whether it conclusively proves or disproves a case.

  • Causes of Inadmissibility: Improper collection protocols, violation of constitutional rights (such as unlawful search and seizure), breach in the chain of custody, contamination, or prejudicial bias.

• Admissible Evidence:

  • Definition: Evidence that satisfies all relevant legal requirements and can be formally presented before a judge or jury.

  • Criteria for Admissibility:

  1. Legitimately Collected and Maintained: Gathered in full compliance with legal search procedures and maintained under strict chain-of-custody protocols.

  2. Pertinent: Directly relevant and material to the specific facts of the case.

  3. Non-Prejudicial: Its probative value outweighs any unfair prejudice, confusion, or misleading effect on the court.