Crime Scene Investigation (Forensic Science: The Basics)

Flashcards covering key concepts from the Crime Scene Investigation notes, including chain of custody, MO/PMI, documentation, search methods, evidence collection, packaging, and notable case examples.

What is the chain of custody and what does it document?

A physical log for a single piece of evidence that documents who had possession of the evidence and when; a flowchart of its movement from collection to court, ensuring the integrity of the evidence.

What does corpus delicti mean and why is it important?

The body of crime; proof that a crime occurred before conviction (e.g., a death must be ruled a homicide before murder charges).

What are exemplars (knowns) in evidence collection?

Baseline, known evidence such as fingerprints, DNA, hair, or voiceprints used for comparison with scene evidence; also called controls.

Who is the first responder at a crime scene and what are their initial duties?

The initial police officer on scene (first responder); duties include determining if the perpetrator is still present, tending to the injured, notifying supervisors, securing consent or warrants, securing the scene, and noting hazards to prevent contamination.

What does MO stand for and how is it used in investigations?

Modus operandi; the pattern or method a criminal uses; helps investigators link multiple crimes to a suspect by recognizing distinctive behavior.

What is PMI in forensic terms?

Postmortem interval; the length of time from death to discovery of the body.

What does probative mean in legal evidence?

Evidence that tends to prove or disprove a fact or assertion in a case.

What is a crime scene protocol?

An established, detailed plan or procedure that must be followed for evidence to be valid and admissible in court, ensuring consistent investigations.

Name four basic crime scene search methods.

Spiral, grid, line, and zone searches.

What is the purpose of documentation at the crime scene?

To record in detail the conditions when the crime occurred, including the labeling and location of evidence to preserve the scene’s history.

What are the three major steps in evidence collection?

Recognition of evidence, collection, and packaging/preservation.

What is tamper-evident packaging and why is it important?

Packaging that seals and can only be opened by tearing or cutting, leaving visible signs of access; ensures evidence integrity and traceability; sometimes supplemented with tamper-evident tape.

What is a druggist’s fold (evidence fold) used for?

A folded piece of paper used to securely hold small pieces of evidence before placing them in a bag or envelope, preventing loss.

What is the purpose of exemplars in comparisons (fingerprints, DNA, etc.)?

Known evidence from suspects or victims used for comparison with crime scene evidence to link or exclude individuals.

What is a sting operation in law enforcement?

A proactive operation where officers stage scenarios to encourage criminals to commit crimes they would likely commit, yielding evidence and arrests.

What is the plan of attack in crime scene searches?

A systematic plan for searching the site to ensure no area is overlooked while avoiding unnecessary repetition.

List safety and control considerations at a crime scene.

Identify hazards, minimize contamination by limiting access, determine entry/exit routes, and secure a perimeter to protect evidence.

What is a preliminary scene examination?

Initial CSI assessment to determine scene boundaries, safety hazards, potential primary/secondary crime sites, and MO considerations.

What is a systematic search and why is it necessary?

A meticulous process to minimize scene alteration while ensuring evidence is found; involves early photography and selecting an appropriate search pattern.

What are the four general search patterns (as shown in Figure 2.2)?

Spiral, grid, line, and zone.

What is the role of photography in crime scene documentation?

Digital photos are preferred for immediacy and integration into reports; videos/walk-throughs can be used; audio is muted to avoid influencing juries; photos are taken at full scene, then distance, mid-range, and close-up with/without scale.

What is a Total Station and why is it used?

A laser rangefinder and computer system used to capture precise 3D measurements, coordinates, and angles of a crime scene for reconstruction.

How is GPS used in documenting crime scenes?

To mark coordinates and document locations in remote or wooded areas where fixed reference points are unavailable.

What is reconstruction in crime scene investigation?

The process of reconstructing the crime to identify victim(s) and perpetrator(s), determine the sequence of events, and link the suspect to the crime through evidence.

What are the three major steps in evidence collection (revisited)?

Recognition of evidence, collection, and packaging/preservation (followed by delivery to the lab for analysis).

What is the importance of preserving evidence and chain of custody?

Maintaining integrity through tamper-evident packaging and a custody log to ensure admissibility; any break can render evidence inadmissible.

What does a forensic pathologist do at a crime scene?

Certifies death, determines PMI, and may oversee the body’s handling and transport to the medical examiner’s or coroner’s lab.

What should be considered when packaging trace evidence?

Place trace evidence (hair, fiber, glass) in envelopes or baggies; avoid tape lifts that can contaminate or contaminate chemical analyses.

What were key pieces of evidence in the Richard Crafts case that linked him to Helle Crafts’ murder?

Human tissue, bone fragments, hair, fibers, blood, dental crown matching Helle’s, and a chain saw with a serial number linked to Crafts; woodchipper and lake evidence corroborated the crime.

Why are differential packaging requirements used for living plants, biological fluids, paint, and fire residues?

Different substances require specific conditions to prevent degradation: breathable containers for plants and wet biologicals, EDTA-preserved or dry specimens for blood, breathable envelopes for trace evidence, airtight containers for fire residues.