Forensics & Analytical Techniques Lecture Review

Vocabulary flashcards covering fingerprint development and patterns, blood-spatter analysis, glass fracture, DNA profiling, chromatography, chemical tests for sugars, hair examination, polymer identification, and core analytical techniques mentioned in the lecture notes.

Cyanoacrylate (Superglue) Fuming

Fingerprint development method for non-porous surfaces; vapors polymerize on print residues, producing a sticky white (often dyed purple) ridge pattern.

Iodine Fuming

Early vapor-phase fingerprint technique; iodine crystals sublime and temporarily react with fats/oils in latent prints to reveal brown ridges.

Ninhydrin

Chemical that reacts with amino acids in latent prints on porous materials (e.g., paper) to produce a purple-blue (Ruhemann’s) coloration.

Small Particle Reagent (SPR)

Suspension applied to wet, non-porous surfaces; particles adhere to lipid components of fingerprints, creating gray/black ridges.

Regular Fingerprint Powder

Fine non-magnetic powder brushed onto many household or vehicle surfaces; adheres to print oils, then lifted with tape.

Magnetic Fingerprint Powder

Powder containing iron; applied with a magnetic wand to shiny plastics/metals, minimizing brush contact and background debris.

Latent Fingerprint

Invisible ridge impression left by skin secretions; usually requires chemical or powder processing for visualization.

Visible Fingerprint

Print easily seen with the naked eye because the fingers were coated with a colored substance such as blood, paint, or ink.

Impression Fingerprint

Three-dimensional print left in soft material (e.g., clay, wax, fresh paint) that can be photographed or cast directly.

Dusting (Fingerprint Recovery)

Process of applying powder to latent prints, then lifting the developed image with adhesive tape for lab examination.

Bifurcation (Minutiae)

Fingerprint feature where one ridge splits into two branches.

Ridge Ending

Point where a fingerprint ridge terminates abruptly.

Island (Dot)

Very short ridge or single dot-like feature within a fingerprint pattern.

Loop

Most common fingerprint pattern; ridges enter from one side, curve, and exit the same side (ulnar or radial).

Whorl

Fingerprint pattern consisting of one or more circular or spiral ridges with two deltas.

Arch

Least common fingerprint pattern; ridges enter from one side and exit the other, forming a wave-like pattern (plain or tented).

Angle of Impact (Blood Spatter)

θ = arcsin (W⁄L); determines the angle at which a blood droplet struck a surface, using width (W) and length (L).

Low-Velocity Blood Spatter

Large, drop-like stains formed at <5 ft/s; usually dripping blood.

Medium-Velocity Blood Spatter

Linear or clustered droplets produced at 5–25 ft/s, often from blunt-force trauma.

High-Velocity Blood Spatter

Fine mist-like pattern created around 100 ft/s, typical of gunshots or explosions.

3Rs of Glass Fracture

“Radial cracks at Right angles to the Reverse side of impact” – aids in determining force direction.

Refractive Index (Glass)

Ratio of light speed in vacuum to that in glass; if it matches the surrounding liquid, the glass fragment becomes nearly invisible.

Radial Crack

Fracture lines that radiate outward from the point of impact in glass.

DNA (Deoxyribonucleic Acid)

Double-helix polymer of nucleotides that carries genetic information; bases are adenine, thymine, guanine, and cytosine.

Nucleotide

DNA subunit composed of deoxyribose sugar, phosphate group, and a nitrogenous base.

Gel Electrophoresis

Technique that separates DNA fragments by size through an agarose matrix under an electric field; forms the basis of DNA fingerprinting.

Adenine–Thymine Pairing

Complementary base pairing in DNA held by two hydrogen bonds.

Guanine–Cytosine Pairing

Complementary base pairing in DNA held by three hydrogen bonds.

Chromatography

Separation method where components partition between stationary and mobile phases; used for ink analysis and purification.

Chromatogram

Visual output of chromatography showing separated bands or spots of mixture components.

Benedict’s Test

Chemical test for reducing sugars; heating with Benedict’s reagent yields a green-to-brick-red precipitate proportional to sugar concentration.

Fehling’s Test

Copper(II) tartrate solution that forms a red precipitate in the presence of reducing sugars; blue remains if negative.

Reducing Sugar

Carbohydrate with a free aldehyde or α-hydroxy-ketone group capable of reducing Cu²⁺ to Cu⁺ in Benedict’s or Fehling’s tests.

Medulla (Hair)

Central core of a hair shaft; width contributes to medullary index used to distinguish human vs. animal hair.

Cortex (Hair)

Main body of hair containing pigment granules and providing strength and color.

Cuticle (Hair)

Outer, scale-like layer of overlapping cells pointing from root toward tip; protects the hair shaft.

Medullary Index

Ratio of medulla diameter to entire hair diameter; >0.5 indicates animal hair, <0.33 indicates human hair.

Anagen Phase

Active growth stage of hair lasting 3–5 years.

Catagen Phase

Short transitional stage of hair growth lasting about 3 weeks.

Telogen Phase

Resting stage of hair growth (~3 months) culminating in natural shedding.

PETE (Polyethylene Terephthalate)

Type 1 plastic; clear, strong polyester used for beverage bottles and food packaging.

HDPE (High-Density Polyethylene)

Type 2 plastic; rigid petroleum-based polymer used for milk jugs, detergent bottles, and plastic lumber.

LDPE (Low-Density Polyethylene)

Flexible, translucent Type 4 plastic used in grocery bags, plastic wrap, and film.

PC (Polycarbonate)

Strong, impact-resistant plastic for eyewear lenses, medical devices, CDs/DVDs, and protective gear.

PMMA (Polymethyl Methacrylate)

Lightweight, shatter-resistant glass alternative used in windows, aquariums, and medical implants.

Spectroscopy

Analytical technique that identifies or quantifies substances by their characteristic interaction with electromagnetic radiation.