Forensic Science: Locard's Principle & CSI Basics

Goals of CSI

• Recognize, document, and collect evidence at crime scenes.

Locard's Exchange Principle

• Proposed by Edmond Locard.
• States that contact between two objects leads to a cross-transfer of physical evidence.
• The extent of transfer depends on the intensity, nature, and duration of the materials involved.

Types of Evidence

• Direct Evidence: Eyewitness accounts, videos, and confessions are considered direct proof of a crime.
• Circumstantial Evidence: Implies or infers a fact but does not directly prove it, such as finding a gun at a scene suggesting a suspect's presence.

Categories of Circumstantial Evidence

• Three main types: physical, biological, and trace evidence.
• Can be classified as either individual (specific to one source) or class (common to a group).

Physical and Biological Evidence

• Physical Evidence: Tangible items collected from a crime scene.
• Biological Evidence: Material from living beings, such as hair, blood, or other bodily fluids.

Trace Evidence

• Refers to small but measurable amounts of physical or biological material found at a crime scene, which can be either physical or biological in nature.

Individual and Class Evidence

• Individual Evidence: Can be linked to a single individual with high certainty, such as a matching bullet to a suspect's gun.
• Class Evidence: Associated with a group, such as a blood type or a type of fabric.

Importance of Evidence

• Can prove a crime, back up or disprove a witness, link a suspect to a victim, determine identities, and help reconstruct the crime.

Evidence Types Specifications

• Direct evidence can only be testimonial; it cannot be categorized as physical, biological, individual, or class evidence.

Role of CSI Team Members

• Initial responding officers, backup police, medics, investigators, medical examiners, photographers, field evidence technicians, and lab experts make up a CSI team.

Seven S's of CSI Process

• Secure the scene, separate witnesses, scan the scene, see the scene, sketch the scene, search for evidence, and secure and collect evidence.

Securing the Scene

• The first officer must ensure the area is isolated and call for specialists after addressing any immediate medical needs or apprehending suspects.

Separating Witnesses

• Important to prevent collusion by asking each witness six key questions.

Scanning the Scene

• Assess where photos should be taken and identify primary and secondary scenes.

Seeing and Documenting the Scene

• Photography should be done both close-up and with measuring rulers for context.

Sketching the Scene

• Create accurate representations of physical facts, understand event sequences, and mark locations of objects.
• Include rough and finished sketches, label north (N), and use a scale. Measurements should be referenced from immovable objects, such as walls.

Explore the fundamentals of forensic science with a focus on Locard's Exchange Principle and the foundational Seven S's of Crime Scene Investigation. This quiz covers essential terminology and concepts crucial for understanding crime scene protocols and evidence handling.