Forensic Science Comprehensive Study Notes

Overview / Intro

  • Forensic Science = application of science to criminal & civil law.
    • Broad: any science for law-enforcement.
    • Specific: techniques enforced by police within the justice system.
  • CSI Effect
    • Public (esp. jurors) believe every scene yields conclusive physical evidence → sets unrealistically high expectations.
  • Historical roots
    • Sir Arthur Conan Doyle’s Sherlock Holmes predicted future techniques (serology, firearms ID, fingerprints, questioned docs).

Pioneering Scientists & Their Contributions

  • Mathieu Orfila – father of toxicology; animal-poison studies.
  • Alphonse Bertillon – anthropometry (body-length measurements); first ID system.
  • Francis Galton – first statistical study + classification of fingerprints; wrote first FP textbook.
  • Karl Landsteiner – discovered ABO blood groups.
  • Leone Lattes – method to determine blood groups from dried stains.
  • Calvin Goddard – firearms/ballistics pioneer; co-developed comparison microscope.
  • Albert Osborn – father of questioned-document examination.
  • Walter McCrone – leading light-microscopy expert.
  • Hans Gross – wrote on applying science to crim. investigation.
  • Edmond Locard – Locard Exchange Principle: “Every contact leaves a trace”; founded 1st crime lab.

Crime-Lab Units & Functions

  • Physical Science Unit – physics/chemistry/geology; drug ID, glass, explosives, soil.
  • Biology Unit – DNA, blood, body fluids, hair, botanical material.
  • Firearms Unit – bullets, casings, toolmarks; GSR on garments.
  • Document Examination – handwriting, typewriting, paper, ink, erasures.
  • Photography – digital, IR, UV, X-ray imaging, evidence logging.
  • Optional Units
    • Toxicology – poisons, drugs in organs/fluids; instrument training.
    • Latent Fingerprint – develop & preserve latent prints.
    • Polygraph – lie-detector exams.
    • Voiceprint – audio/telephone threats; spectrography.
    • Crime-Scene Unit – evidence collection team.
  • Communication lines among units must stay open.

Evidence Typology

  • Class characteristics – shared by a group (soil, hair, blood type).
  • Individual characteristics – unique, random, traceable to single source (fingerprints, DNA, striations on bullet).
  • Wear patterns – between class & individual; surface erosion narrows source pool but not unique.

Criminalist / Forensic Scientist

  • Collects, preserves, analyzes physical evidence; testifies as expert.

Legal Standards, Courtroom Admissibility & Warrants

  • Frye – state level; technique must be “generally accepted” → Frye hearing can be requested pre-trial.
  • Daubert – federal; judge = “gatekeeper”; considers \text{error rate},\,\text{peer review},\,\text{general acceptance},\,\text{relevance}.
  • Expert Witness Qualifications
    • Education, experience, publications, professional memberships; opinion testimony allowed after voir dire.
  • Miranda – custodial interrogation triggers warnings.
  • Warrant exceptions
    • Exigent circumstances, probable loss of evidence, officer safety, probable cause, plain view.

Crime-Scene Management

  • First officer priorities: safety & medical aid → detain suspects/witnesses → secure & isolate scene.
  • Boundaries must include entry/exit paths & probable evidence zones.
  • Log all personnel; only investigators inside tape.
  • Documentation: notes, photos, video, sketches.

Evidence Collection Protocols

  • Package trace sources intact (clothing, bedding).
  • Bag garments separately; paper over plastic for biologics.
  • Vacuum critical areas individually; collect fingernail scrapings.
  • Change gloves between exhibits – discarded gloves = evidence.
  • Reference/standard samples: controls for comparison (e.g. victim’s hair, surface paint).
  • “One-chance” mindset – never discard potential evidence.

Crime-Scene Sketching

  • Rough sketch on-scene: accurate measurements with tape; objects lettered/numbered; compass rose; title block.
  • Finished sketch later (often digital).
  • Mapping methods
    • Triangulation – two fixed points to object.
    • Baseline – tape baseline + right-angle offset for large open areas.

Physical-Evidence Significance

  • Probability/rarity governs weight.
  • Class traits weaker than individual; databases (AFIS, CODIS, etc.) & examiner experience crucial.

Fingerprints

  • Skin anatomy: epidermis, dermis, dermal papillae → permanent ridge pattern; pores = sweat gland ducts.
  • Sweat composition: \text{H}_2\text{O},\,\text{fatty acids},\,\text{salts},\,\text{proteins}.
  • Print types
    • Latent – invisible residue; need development.
    • Visible – blood, paint, grease.
    • Plastic – impressed in soft medium.
  • Pattern classes
    • Loop (1 delta), Whorl (2 deltas), Arch (0 deltas).
  • Identification: minutiae – ridge endings, bifurcations, islands, enclosures; no fixed minimum points (1973 IAI).
  • ACE-V methodology: Analysis → Comparison → Evaluation → Verification; beware confirmation bias (e.g., Madrid bombing mis-ID).
  • Alterations: permanent scarring 1\text{–}2\,\text{mm} below surface can change ridges.

Development / Lifting Techniques

  • Powder dusting (magnetic, traditional) on hard, nonporous.
  • Iodine fuming – reacts with lipids (temporary, brown) on paper.
  • Ninhydrin – reacts with amino acids → purple-blue (porous, aged prints up to \ge 15 yrs).
  • Silver nitrate – last resort; reacts with \text{Cl}^-; UV → brown/black; destroys proteins.
  • Cyanoacrylate fuming – super-glue vapor polymerizes on residues → permanent white.
  • Fluorescence w/ ALS or lasers; chemicals like LCV, amido black enhance bloody prints.
  • Photograph before tape-lift; label lift card.

Databases

  • AFIS / IAFIS – fingerprint minutiae.
  • CODIS – DNA; three indexes (Forensic, Offender, Missing).
  • NIBIN – ballistics (brass & bullets).
  • SICAR – shoeprints.
  • PDQ – automotive paint.

9/11 World Trade Center Case Study

  • 4 hijacked flights (11/09/2001); 3 targets hit (Towers 1 & 2, Pentagon); 4^{th} crashed in PA after passenger revolt.
  • \gt 3000 fatalities; debris → Freshkills Landfill for hand-sorting.
  • Responders treated site as giant crime scene; GPS-plotting, evidence bagging (#DM tags).
  • Victim ID hierarchy: 1) Odontology (dental), 2) DNA (family reference, WinID dental AFIS, DMORT teams).
  • Spurred creation of Homeland Security.

Death Investigation & Forensic Pathology

  • Forensic pathologist – MD performing autopsy; certifies cause/manner.
  • Cause vs. Manner
    • Cause = medical reason (exsanguination, MI, GSW).
    • Manner = legal classification: Homicide, Suicide, Accident, Natural, Undetermined.
  • Autopsy steps
    • External exam, photography, fingerprints, clothing evidence.
    • Y-shaped thoraco-abdominal incision; weigh organs; collect samples (blood, urine, vitreous, gastric contents, CSF).
    • Examine eyes for petechiae (strangulation).
    • Skull opened for brain exam.
  • Medicolegal Investigator (MLI) – scene/body evidence liaison; may be coroner, ME, anthropologist, etc.
  • Post-mortem changes
    • Rigor mortis: onset 2 h, full 12 h, gone \approx36 h.
    • Livor mortis: pooling begins \approx 30 min; fixed 6\text{–}8 h.
    • Algor mortis: cooling toward ambient; “1\,^{\circ}\text{F} per hr” rule if average clothing/weight/temp.
    • Autolysis → Putrefaction → Active decay → Dry/remains.
    • Special phenomena: Saponification/adipocere (soap wax), mummification (dry heat), bone diagenesis.
  • Vitreous humor: durable matrix for ethanol, electrolytes.
  • Crescentic nail abrasions: horizontal (victim), vertical (assailant from rear).

Forensic Photography Basics

  • Goal: truthful, objective, admissible images; maintain chain of custody & photo log.
  • Exposure triangle: aperture (f-stop), shutter speed, ISO (sensor sensitivity).
    • Large f-number → small aperture → less light; affects depth of field.
    • Fast shutter \rightarrow freezes motion but dark; slow \rightarrow brighter, risk blur.
  • Depth of field: shallow isolates subject; large captures scene.
  • Alteration vs. enhancement: adjustments (brightness, crop) allowed if originals preserved + steps logged.
  • Digital concerns (initially): security, cost, court admissibility; Frye hearings resolved.
  • File formats: JPEG (compressed), TIFF/RAW (lossless, 3× larger, preferred for micro detail).
  • Macro: close-up (prints, casings); ensure scale & subject on same focal plane; ABFO “L” scales.
  • Lighting: fill flash, backlighting, IR for contrast; photograph crowds (unsub may watch).
  • Procedure: • overall → midrange → close-ups, with & without scale, hourly bloodstain shots (time + ambient temp), document approach/exit paths.

DNA Biology & Typing

  • DNA = double helix of 3\,\text{billion} base pairs; code for proteins.
  • Humans share 99.9\%; the 0.1\% variation = forensic gold.
  • PCR (polymerase chain reaction) amplifies trace DNA.
  • STR analysis – \le 20 loci; fluorescently tagged; statistical frequency of occurrence calculated.
  • Mitochondrial DNA – matrilineal; useful for hair shafts, degraded samples.
  • Evidence collection: buccal swabs, personal items, parental references, siblings if necessary.

Arson & Fire Investigation

  • Fire tetrahedron: fuel, \text{O}_2, heat, chain reaction.
  • Heat transfer: conduction (solid-solid), convection (gas/liquid cycles), radiation (EM waves).
  • Key temperatures
    • Flashover \approx 1100\,^{\circ}\text{F} – total room ignition.
    • Steel loses 50\% strength \approx 1000\,^{\circ}\text{F}.
  • Definitions
    • Ignition temp – spontaneous combustion threshold.
    • Flash point – lowest temp producing ignitable vapor.
    • Pyrolysis – solid decomposes → combustible gas.
    • Flammable range – vapor/air concentration limits.
    • Glowing combustion – flameless (smoldering).
  • Patterns: V (normal upward spread), inverted V (accelerant/high heat), alligatoring (deep char), pour pattern (liquid accelerant).
  • Fire-scene approach: least-burned → most-burned; two walk-throughs (with 1st officer, then owner).
  • Evidence: collect 2\text{–}3 qt char/ash in airtight paint cans; use accelerant-sniffing canines.
  • Lab analysis: Head-space, charcoal strip, GC-MS (He carrier gas).
  • Victim assessment: soot in trachea, \text{CO} saturation indicates live during fire.
    • Pugilistic stance = heat-induced muscle contraction.
  • Legal degrees of NY arson (5^{th}–1^{st}). 1^{st}: incendiary device/expectation of profit + potential human presence.

Forensic Entomology

  • Life cycle (blowfly): Egg ⇒ 1st instar ⇒ 2nd ⇒ 3rd ⇒ migrating maggot ⇒ pupa ⇒ adult.
    • Timeline (typical 25\,^{\circ}\text{C}): 8\text{–}14 h egg→larva-1; \sim 10\text{–}13 d egg→pupa; 6\text{–}14 d pupa→adult.
  • No oviposition at night, rain, before sunrise, < 50\,^{\circ}\text{F}.
  • Spiracle morphology stages age maggots.
  • Investigator data set: ambient temp, ground surface, 1\,ft & 4\,ft air temps, maggot mass temp; add 48\text{–}72 h if body indoors.
  • Faunal regression: predictable succession of species aids PMI estimate.
  • Evidence: collect live + preserved larvae (species-separated), freeze toxicology samples, supply liver bait for live.

Firearms & Ballistics

  • Caliber (rifled) vs. Gauge (shotgun).
  • Law-enforcement sidearms lack manual safeties; trained to aim center-mass (Article 35 NYS – justified deadly force).
  • Barrel rifling → lands (raised inside, create grooves on bullet) & grooves (cut).
  • Class traits: caliber, land/groove count, twist direction.
  • Individual traits: microscopic striations, firing-pin impression, breechface marks, extractor/ejector marks.
  • Headstamp: maker + caliber on casing base.
  • Gunshot residue (GSR) elements: \text{Sb, Ba, Pb}; primer blowback indicates shooter.
  • Wound terminology
    • Stellate (star) – contact shot to skull, gas expansion.
    • Keyhole – oblique skull entry → oval.
    • Tattooing/stippling – powder burns.
    • Bevelled edge – larger exit defect in bone.
  • Kinetic Energy = \tfrac12 m v^2; cavitation forms temporary & permanent wound cavities.
  • Databases: NIBIN, IBIS.

Impression Evidence (Footwear / Tire)

  • 2-D vs. 3-D; positive (deposit) vs. negative (removal).
  • Dry origin (dust) vs. wet origin (blood, water).
  • Detection: oblique lighting, electrostatic dust lifter (ESDL), powders, chemical enhancement, casting (dental stone), adhesive lifts.
  • Photography: ABFO scale at 90^{\circ}, fill frame, tripod.
  • Comparison
    • Class: size, tread design.
    • Wear: erosion patterns (semi-unique).
    • Individual: cuts, air-bubbles, nicks.
    • Elimination when class/wear/individual don’t match.
  • Test impressions: inkpads on paper, gelatin lifts, transparencies, Identicator.

Key Databases – Quick Reference

  • AFIS / IAFIS – fingerprints.
  • CODIS – nuclear & mtDNA.
  • NIBIN / IBIS – cartridge & bullet images.
  • SICAR – shoeprints.
  • PDQ – vehicle paint.
  • WinID – dental.
  • DMORT – Disaster Mortuary Operational Response Team.

Selected Formulae & Physical Constants

  • Kinetic Energy: KE = \tfrac12 m v^2.
  • Flashover temperature: \approx 1100\,^{\circ}\text{F} (\approx 600\,^{\circ}\text{C}).
  • Rigor timeline: onset 2 h → full 12 h → dissipates \approx36 h.
  • Blowfly timelines: see entomology section.