Forensic Science Unit 1

What is a macroscopic crime scene?

The overall, larger location of a crime containing multiple individual crime scenes (e.g., an entire house, a field, or a bullet-riddled vehicle).

What is a microscopic crime scene?

The specific, localized area focusing on trace, physical evidence within a macroscopic scene (e.g., a specific blood spatter pattern on a wall, bullet casings on the floor, or a mattress containing DNA).

What is a primary crime scene?

The original location where the initial criminal act or primary event actually took place (e.g., the room where a homicide occurred).

What is a secondary crime scene?

Any subsequent location that became associated with the crime after the initial act took place (e.g., the shallow grave site where a body was dumped, or the suspect’s getaway vehicle).

How are crime scenes classified by the types of criminal behavior involved?

They are categorized by the nature of the offense, such as homicide scenes, robbery scenes, sexual assault scenes, arson scenes, or burglary scenes.

How are crime scenes classified by location?

They are categorized by their physical environment, distinguishing between indoor, outdoor, aquatic/underwater, or mobile/vehicular environments.

What is the primary role of the first responding officer?

To secure and isolate the crime scene to preserve its integrity, prevent contamination, remove unauthorized personnel, and assist any injured victims.

What are the six key functions of physical evidence at a crime scene?

1. Identification of suspects (using IAFIS/CODIS). 2. Analysis of unknown substances. 3. Linking scene, victim, and suspect via Locard's principle. 4. Establishing Corpus Delicti (reconstructing the crime). 5. Determining Modus Operandi (MO). 6. Corborating or refuting witness testimonies.

What does "Corpus Delicti" mean in forensic science?

"Body of the crime"—the objective, physical evidence required to prove that a specific criminal act actually took place before anyone can be convicted.

What does "Modus Operandi" (MO) mean?

The specific method of operation, habits, and behavioral patterns a criminal repeatedly uses to commit an offense and avoid detection.

What are the four main types of documentation required for a crime scene?

1. Notes (written logs of all actions and observations). 2. Photography (visual, unaltered records). 3. Sketches (spatial relationships and dimensions). 4. Videography (a continuous narrative walkthrough).

What are the four essential steps/ranges of crime scene photography?

1. Orientation/Overview shots (wide context). 2. Mid-range shots (spatial relationships of evidence). 3. Close-up shots (item details without a scale). 4. Close-up shots with a scale (for precise measurement).

What is the difference between a rough sketch and a final sketch?

A rough sketch is drawn at the scene with actual measurements taken but not to scale; a final sketch is a polished, precise rendering drawn to scale (often via CAD software) used for court presentation.

Name the three primary mathematical mapping methods used for sketches.

1. Triangulation (measuring from two fixed permanent points). 2. Baseline/Rectangular Coordinates (measuring at right angles from a straight line). 3. Polar Coordinates (measuring by angle and distance from a single datum point).

When is a Strip or Parallel search pattern utilized?

Used for large, outdoor open spaces, where a team of searchers walk in straight, parallel lines at even intervals across a designated boundary.

When is a Grid or Double-Line search pattern utilized?

Used for highly thorough searches in outdoor areas; searchers walk parallel lines in one direction, then turn 90 degrees and cross the same area perpendicularly.

When is a Zone or Quadrant search pattern utilized?

Used for indoor crime scenes, complex buildings, or highly chaotic environments; the scene is divided into distinct grids/rooms assigned to specific teams.

When is a Spiral (Inward or Outward) search pattern utilized?

Used mostly for underwater/aquatic scenes, or open areas with a clear central point of interest; searchers follow a circular path moving in or out.

When is a Wheel or Ray search pattern utilized?

Used for small, circular outdoor areas; searchers move outward from a central point along straight lines like spokes on a bicycle wheel.

What is the Link Method search pattern based on?

It is a logic-driven search based on the physical evidence found; finding one piece of evidence dictates the direction and location of the next logical area to search.

What is the core principle of Evidence Collection Theory?

To package and preserve evidence in a manner that ensures it undergoes zero changes, zero contamination, zero cross-transfer, and zero physical degradation from the moment it is collected to the courtroom presentation.

Why must biological evidence (wet blood, saliva, semen) never be stored in airtight plastic containers?

Airtight plastic traps moisture, which rapidly promotes the growth of mold and bacteria, causing the DNA and biological material to completely rot and degrade.

What is the mandatory protocol for packaging wet biological evidence?

The items must be allowed to completely air-dry at room temperature in a secure environment, then packaged in breathable, unsealed paper bags or cardboard boxes.

What is a paper bindle (druggist fold)?

A clean piece of paper folded into a secure, enclosed packet used to safely contain small, loose trace evidence like hairs, fibers, glass shards, or drug powders without leaking.

What are Kapak bags used for in forensics?

Heavy-duty, heat-sealed plastic bags used to secure highly toxic controlled substances (like fentanyl or LSD) and to prevent volatile chemical fumes or accelerants from escaping.

Why are firearms packaged in rigid cardboard boxes using plastic zip-ties?

To completely immobilize the weapon, preventing accidental discharges, protecting handlers, and preserving delicate latent fingerprints or DNA on the surface of the firearm.

What is the Chain of Custody?

A continuous, unbroken written log tracking every single individual who has touched, collected, transferred, or analyzed a piece of evidence, ensuring legal accountability and preventing tampering.

What must be written across the biohazard/evidence tape seal on a package?

The collecting officer's handwritten initials and the exact date/time of sealing, positioned so that any opening of the package will visibly tear the signature.

What happens to evidence in court if the Chain of Custody is broken?

The evidence becomes legally inadmissible in court, as its authenticity and protection from tampering can no longer be verified.

What was the forensic significance of Malaysia Airlines Flight MH370 (2014)?

It highlighted the extreme difficulties of underwater crime scene management, defining search zones across vast, remote aquatic macroscopic environments using satellite data.

What was the forensic significance of the Yvonne Fletcher case (London, 1984)?

Demonstrated how a diplomatic embassy building can function as a microscopic crime scene within a highly sensitive international/political macroscopic jurisdiction.

What was the forensic significance of the Hannah Graham case (Virginia, 2014)?

Showcased the successful integration of digital footprint mapping (surveillance video and cell tower tracking) to narrow down and locate a remote, outdoor secondary crime scene.

What is an exemplar sample?

A known, authenticated reference sample collected from a suspect or victim (e.g., a buccal swab or a deliberate ink fingerprint) used to compare against unknown evidence found at the scene.

What is the difference between individual and class characteristics?

Individual characteristics can link evidence to a single, unique source with near certainty (e.g., DNA or matching ridge details on fingerprints). Class characteristics can only link evidence to a common group or category (e.g., a brand of shoe or a car paint type).

What does the acronym CODIS stand for?

Combined DNA Index System — the FBI's national database used to store, search, and match DNA profiles from convicted offenders and unsolved crime scenes.

What does the acronym IAFIS stand for?

Integrated Automated Fingerprint Identification System — the national computerized system maintained by the FBI for storing and comparing digital fingerprint records.

What is the Locard Exchange Principle?

The foundational forensic law stating that "every contact leaves a trace"—whenever two objects come into contact, a cross-transfer of physical material occurs.

Why must arson or fire debris evidence be stored in airtight, clean paint cans?

To prevent the evaporation and loss of highly volatile chemical accelerants, vapors, and hydrocarbons before laboratory testing can occur.

What information must always be included on an Evidence Tag?

Case number, item inventory number, date and time of collection, precise description of the item, location of recovery, and the name/signature of the recovering officer.

What is cross-contamination and how is it prevented?

The unwanted transfer of material between different pieces of evidence; prevented by wearing fresh PPE (gloves), using clean tools for each item, and packaging items completely separate from one another.