Forensic Science I — Midterm Study Guide

Vocabulary practice flashcards covering fundamental forensic concepts, legal standards, physical/chemical evidence classification, ballistics, trace materials, pathology, and fingerprint analysis.

Forensic Science

The application of science or technology to questions in criminal or civil cases, derived from the Latin forensis meaning 'belonging to the forum' (public debate in a court of law).

Circumstantial Evidence

Facts or circumstances that tend to implicate a person, such as owning a car similar to the one used, threatening the victim, or having motive, means, and opportunity.

Direct Evidence

Tangible items found in a suspect's possession that directly implicate them, such as gloves, a mask, or 'fruits of the crime.'

Collateral Materials

Items that do not directly link a suspect to the crime but provide intelligence regarding their sexual preferences, interests, or hobbies (divided into erotica, educational materials, and intelligence files).

Demonstrative Evidence

Real evidence used to illustrate, demonstrate, or recreate an event in court.

Probative Value

The ability of an item of evidence to yield important clues and prove something material to the investigation.

Corpus Delicti

Proof that a crime actually took place.

Modus Operandi (MO)

A criminal's characteristic method or pattern of operating.

Locard's Exchange Principle

The fundamental tenet stating that whenever two objects come into contact, there is a cross-transfer of physical evidence between them ('every contact leaves a trace').

Class Characteristics

Properties of physical evidence that are shared by a group of objects and place an item into a category rather than tracing it to an individual source (used to include or exclude).

Individual Characteristics

Properties of physical evidence that can be attributed to a single source with an extremely high degree of certainty (e.g., wear marks, striations, or nuclear DNA).

Probable Cause

A practical probability (not absolute certainty) that evidence of a crime will be found in the specific place being searched.

Reasonable Expectation of Privacy

The two-pronged Fourth Amendment standard established in Katz v. United States requiring that a person has an actual expectation of privacy and that society recognizes that expectation as objectively reasonable.

Curtilage

The area immediately surrounding a home that is treated as an extension of the home itself, making it protected by the Fourth Amendment.

Open Fields

Unoccupied or undeveloped land lying beyond the curtilage where Fourth Amendment protections against warrantless searches do not apply.

Exclusionary Rule

A legal rule mandating that evidence obtained in violation of the Fourth Amendment cannot be admitted against a defendant at trial.

Fruit of the Poisonous Tree

A legal doctrine dictating that secondary or derivative evidence obtained as a direct result of an illegal search or seizure is also inadmissible.

Frye Standard

A legal admissibility test requiring that a scientific technique or theory must be generally accepted within the relevant scientific community.

Daubert Standard

An evidentiary rule designating the trial judge as the 'gatekeeper' to determine scientific admissibility based on empirical testing, peer review, error rates, maintenance of standards, and general acceptance.

Voir Dire

The preliminary examination process used in court to qualify an expert witness by evaluating their background, training, and credentials.

Chain of Custody

The documented, continuous possession of evidence proving that an item stayed in substantially the same condition from the time of collection through trial.

Intensive Physical Property

A physical property that depends solely on the chemical identity of the substance, independent of sample size (e.g., density, refractive index, and boiling point).

Extensive Physical Property

A physical property that depends directly on the amount of material present (e.g., mass, volume, and length).

Density Gradient Tube

A comparative analytical technique where two glass tubes containing layered liquids of varying densities are used to observe where suspended soil particles float.

Algor Mortis

The postmortem cooling of the body toward ambient temperature, estimated to drop at a rate of approximately $1.5\,^\circ\text{F}$ ($\approx 0.8\,^\circ\text{C}$) per hour under average conditions.

Rigor Mortis

The postmortem stiffening of skeletal muscles that begins within $2\text{--}6\text{ hours}$, reaches full development at approximately $12\text{ hours}$, and subsides after $24\text{--}36\text{ hours}$.

Livor Mortis

The postmortem settling and pooling of blood in lower tissues due to gravity, which typically becomes fixed after approximately $8\text{--}12\text{ hours}$.

Caliber

The internal diameter of a firearm bore measured land-to-land in hundredths of an inch (such as $.22$, $.38$, or $.45$) or millimeters (such as $9\,\text{mm}$).

Rifling

The spiral arrangement of raised ridges (lands) and cut channels (grooves) inside a barrel that impart spin to a bullet for flight stability and accuracy.

Comparison Microscope

An optical device consisting of two compound microscopes linked by an optical bridge, invented by Philip Gravelle to allow simultaneous, side-by-side comparison of fired bullets, casings, hairs, or fibers.

IBIS (Integrated Ballistic Identification System)

An automated computer imaging system that captures digital images of fired bullets and cartridge casings to screen for potential matches within the NIBIN network.

Internal Ballistics

The phase of ballistics studying events occurring entirely inside the firearm, including firing pin strikes, powder ignition, and the bullet passing through rifling.

External Ballistics

The phase of ballistics analyzing the flight of a projectile from the moment it leaves the barrel until it impacts a target.

Terminal Ballistics

The phase of ballistics examining what happens when a projectile strikes its target, including wound profiles, bullet deformation, and fragmentation.

Primer Gunshot Residue (PGSR)

Microscopic, molten-looking particles typically measuring $1\text{--}5\,\mu\text{m}$ that escape firearm openings upon discharge and contain the characteristic elemental signature of lead ($\text{Pb}$), barium ($\text{Ba}$), and antimony ($\text{Sb}$).

Randomly Acquired Characteristics (RACs)

Unplanned, random alterations to footwear soles, tire treads, or tool edges—such as cuts, scratches, embedded rocks, or nicks—that allow an examiner to individualize an impression.

Passive Bloodstain Drops

Bloodstains created by the force of gravity acting alone on blood, producing drops that are usually $4\,\text{mm}$ or larger in diameter.

Impact Spatter

A pattern formed when an object forcefully strikes liquid blood, resulting in stain diameters of $1\text{--}4\,\text{mm}$ from beating or stabbing, or mist-like stains $\le 1\,\text{mm}$ from gunshots or high-energy impacts.

Cast-Off Pattern

Blood drops released or flung from a moving, bloodied weapon or object during a swing arc, generating linear or curved trails.

Arterial Gush (Spurt)

A projected bloodstain pattern caused by blood escaping under systemic pressure from a damaged artery, characterized by large, arcing or zig-zag wave stains that fluctuate with heartbeats.

Void Pattern

An unstained space within an otherwise continuous bloodstain pattern, indicating that an intervening object or person intercepted the spatter and was subsequently removed.

Luminol

A presumptive chemical reagent that reacts with the iron in the heme group of hemoglobin to produce a chemiluminescent blue glow in low-light conditions.

Anagen Phase

The active growth phase of a hair follicle during which the root bulb is firmly attached to cellular tissue, serving as the prime source for nuclear DNA extraction.

Telogen Phase

The final resting and shedding phase of a hair where the root forms an inactive club shape lacking follicular tissue, yielding primarily mitochondrial DNA rather than nuclear DNA.

3R Rule

A forensic glass fracture rule specifying that Radial cracks form Rib (stress) marks at Right angles to the Reverse side (the surface opposite the applied force).

Abrasion

A blunt-force superficial scrape on the outer layers of the skin, which can indicate the direction and patterned contour of the impacting object.

Contusion

A blunt-force injury caused by the rupture of subcutaneous blood vessels without disrupting skin continuity, appearing as a bruise.

Laceration

A blunt-force injury where skin tears apart under tension or crushing force, characterized by ragged edges, abraded margins, and intact tissue bridging across the wound gap.

Incised Wound

A sharp-force wound caused by a keen blade drawn along the skin that is longer than it is deep, featuring clean, unbruised margins with no tissue bridging.

Stab Wound

A sharp-force puncture wound produced by thrusting a pointed instrument into the body, resulting in an injury that is deeper than its surface length.

Penetrating Wound

A gunshot wound in which the projectile enters the body and comes to rest internally without creating an exit wound.

Perforating Wound

A gunshot wound in which the bullet enters the body and passes entirely through, producing both an entrance and an exit wound.

Dynamic Loading

Blunt-force trauma delivered rapidly within a duration under approximately $0.2\,\text{s}$, such as an impact blow from a bat or a collision.

Static Loading

Blunt-force trauma applied gradually over a duration exceeding approximately $0.2\,\text{s}$, typically causing severe comminuted crushing fractures (such as head pinning beneath a heavy vehicle).

Bertillon System (Anthropometry)

An early system of criminal identification invented by Alphonse Bertillon based on specific anthropometric body measurements and photographs, which was discredited by the Will West and William West incident in 1903.

Plastic Fingerprint

A three-dimensional impression molded into a pliable, soft material such as wax, putty, clay, soap, or wet paint.

Patent Fingerprint

A visible two-dimensional friction ridge impression deposited onto a surface through contact with a colored medium such as blood, paint, grease, or ink.

Latent Fingerprint

An invisible friction ridge pattern composed of deposited sweat and sebaceous oils left on a surface, requiring optical, physical, or chemical visualization techniques.

Cyanoacrylate Fuming

A chemical development technique where heated superglue vapors react with traces of moisture and amino acids to produce an off-white, stable polymer print on non-porous surfaces.

Ninhydrin

A chemical reagent used on porous substrates like paper that reacts with amino acids in latent residue to yield a colored product called Ruhemann's purple.