Principles & Legal Standards
What core forensic rule states that whenever two objects come into contact, a cross-transfer of physical material occurs?
Locard's Exchange Principle
What type of evidence narrows a suspect's identity down to a single specific person or source?
Individual evidence
What broad category of evidence includes firsthand testimonies, victim accounts, confessions, or direct video recordings that prove a fact without needing an inference?
Direct evidence
What is the very first step out of the "7 S's of Crime Scene Investigation" that a responding officer must perform?
Secure the scene
What is the Chain of Custody?
The documented, unbroken transfer log ensuring legal security, trackable responsibility, and integrity of evidence.
Under the Daubert Standard (1993), who serves as the ultimate "gatekeeper" evaluating whether expert testimony and scientific techniques are admissible in court?
The trial judge presiding over the courtroom
What type of evidence connects a suspect or item to a broader group or mass-produced batch, but cannot single out an individual alone?
Class evidence
What category of indirect evidence implies a fact but requires a judge or jury to infer a connection (e.g., finding a suspect's fingerprint at a scene)?
Circumstantial evidence
Why is "Separating Witnesses" a critical early step during crime scene processing?
To prevent witnesses from talking to each other, colluding, or altering/distorting each other's memories of the event.
How must a forensic laboratory technician properly open a sealed evidence bag to maintain the Chain of Custody?
The technician must cut open the bag at a location other than the original collector's signed tamper-evident tape seal.
According to the second part of Locard's Exchange Principle, what factors determine the extent and quantity of material transferred during contact?
The intensity, duration, and nature of the physical contact
True or False: ABO blood typing is considered individual evidence because a person's blood type uniquely identifies them.
False. Blood typing is class evidence because multiple people share the same blood type
Fingerprints, tire impressions, weapons, and bullet casings are classified under which subcategory of circumstantial evidence?
Physical evidence
What key details must be included when creating a crime scene sketch?
Distances measured from two fixed landmarks, marking Magnetic North, and including an exact scale/key.
What happens if a lab technician tears directly through the original collector's signed seal or fails to log the transfer of an evidence bag
The Chain of Custody is broken, making the evidence vulnerable to defense arguments of tampering or contamination, rendering it potentially inadmissible in court.
What is a paper bindle, and what type of evidence is it designed to safely hold?
A folded paper container used to safely package small, dry trace evidence without loss.
Name two real-world examples of class evidence and two real-world examples of individual evidence.
Class evidence: ABO blood typing, general hair without root, soil, mass-produced fiber. Individual evidence: DNA profile, unique fingerprint minutiae.
Body fluids, hair, plant parts, and natural fibers fall under which subcategory of circumstantial evidence?
Biological evidence
List all seven steps of crime scene investigation (the 7 S's) in sequential order.
1. Secure the scene, 2. Separate the witnesses, 3. Scan the scene, 4. See (photograph) the scene, 5. Sketch the scene, 6. Search for evidence, 7. Secure and collect evidence.
What is crime scene reconstruction?
Forming a hypothesis of the sequence of events before, during, and after a crime was committed using forensic evidence and lab results
Why is sealing a damp or wet biological sample (like blood) directly inside an airtight plastic bag a major procedural violation?
Trapped moisture fosters mold and bacterial growth, destroying DNA and biological evidence.
How does the statistical weight or match strength differ between class evidence and individual evidence?
Class evidence provides group-level probability, whereas individual evidence provides an extremely high statistical probability match (often exceeding 1 in 1 billion).
What is trace evidence? Give three examples.
Small but measurable amounts of physical or biological material transferred at a scene. Examples: Strands of hair, clothing fibers, glass fragments, paint chips, drop of blood/saliva.
Describe two major procedural errors made by first responders in the initial 1996 JonBenét Ramsey homicide investigation and their forensic consequences.
Responders only sealed off the victim's bedroom rather than securing the entire home, allowing the rest of the crime scene to be contaminated or destroyed.
Family members and visitors moved freely through the home and moved/covered the victim's body with a blanket before processing, contaminating evidence and losing trace material.
What does a staged crime scene mean, and what are two common examples of staged scenes?
A staged scene is when evidence is altered to make the crime look like a different event to cover up the truth or deceive investigators. Examples: Staging a fire to cover bankruptcy, staging a suicide to cover a murder, or staging a burglary for insurance money.