Latent Print Development Techniques – Lecture 2 Comprehensive Notes

Overview of Today’s Session

  • Focus topics: latent print development techniques, fingerprint recording, lab books, Lab 1 review, camera kits.
  • Emphasis on techniques used routinely in daily examinations while acknowledging many infrequently used methods.
  • Key message: do not rush; success depends on careful preparation, consultation of reference material, and systematic processing.

Core Sources Referenced

  • “The Fingerprint Source Book.”
  • Canadian Friction Ridge Working Group (CanFRWG) resources.
    • Website: www.canfrwg.ca
    • CanFRWG Slide Library 4.0 (English, 2021-01-01, pptx).

Fingerprint Types & Definitions

  • Visible / Patent Prints
    • Readily seen with the unaided eye.
    • Preserved primarily through photography.
    • Enhanced search with white light or ALS.
  • Latent (Invisible) Prints
    • Require a physical or chemical process to become visible.
    • Processes enhance residue; prints then captured via photographs or tape lifts.
  • Plastic (Moulded) Prints
    • Three-dimensional reverse impressions ("take-away").
    • Found in clay, putty, wax, soft food, etc.
    • Usually visible; documented via photos + possible casting.
  • Usage note: All three are often colloquially called “latent,” but this is technically incorrect.

Surface Categories

  • Porous Substrates
    • Absorbent; residue may penetrate surface.
    • Examples: paper, cardboard, unfinished wood.
    • Prints are relatively durable.
    • Amino-acid reagents (ninhydrin, indanedione, DFO) suited.
  • Non-Porous Substrates
    • Repel moisture; normally polished or shiny.
    • Examples: glass, metal, plastic, painted wood.
    • Prints less durable; rely on cyanoacrylate (CA), powders, dyes, VMD.

Systematic Process Selection

  • Initial visual & ALS inspection with detailed notes/photos.
  • Plan sequential processing (e.g., indanedione → ninhydrin) and document after each stage.
  • Trial-and-error and prior experience guide technique order.

Factors Affecting Technique Choice

  • Suspected residue composition (eccrine, sebum, etc.).
  • Substrate type, texture, cleanliness, and condition.
  • Ambient environment (temperature, humidity, wet vs. dry).
  • Destructive vs. non-destructive consequences.
  • Need for later examinations (e.g., DNA sampling requirements).
  • Proper sequence (e.g., CA fuming before fluorescent dye).
  • Crime seriousness can dictate resource allocation.

Porous Surface: Chemical Techniques

  • Use ALS at multiple stages; follow correct sequencing.

Ninhydrin *

  • Application: dip or spray, then apply heat/humidity (60−70%)(60{-}70\%).
  • Reacts with amino acids/proteins in eccrine residue.
  • Produces magenta → deep purple (“Ruhemann’s Purple”).
  • Standard baseline reagent for porous items.

Indanedione *

  • Dip/bake method; reacts with amino acids.
  • Initial faint pink; fluoresces strong yellow under 515–570 nm with orange/red barrier filter.
  • Exhibits high colour + fluorescence sensitivity.
  • Can follow ninhydrin without conflict.

DFO (1,8-Diazafluoren-9-one)

  • Dip/spray → dry → oven.
  • Amino-acid reaction; produces pink or fluorescent yellow.
  • Visualize/photograph under ALS with orange/red filter.

Physical Developer (PD)

  • Multi-bath immersion protocol (pre-wash, develop, three post-washes).
  • Targets lipids, fats, waxes; yields grey deposit.
  • Suited for water-soaked or extremely aged paper (currency, documents).
  • Time-consuming and considered destructive.

ALS Equipment Notes

  • Poli-Light (handheld/portable): multiple wavelengths, evidence-safe, cost dropping.
  • Portable laser: single wavelength, potential evidence damage if misused, smaller & cheaper today.
  • Always follow health & safety protocols.

Non-Porous Surface Techniques

  • Typical items: bottles, hard plastics, metals, firearms, knives, licence plates.

Brushes Overview

  • Fibreglass: standard granular powders.
  • Squirrel/Camel hair: gentle cleaning, light powders.
  • Feather duster: ultra-fine & fluorescent powders.
  • Magnetic wand: applies magnetic powders.

Granular Powders *

  • Carbon-based mixtures; multiple colours.
  • Adhere to moisture/oils; risk of abrasion or “fill-in” if over-applied.
  • Always test small area for contrast & adherence; monitor cross-contamination.

Fluorescent Powders

  • Extremely fine; applied with feather brush.
  • Require ALS for viewing; proper PPE essential.
  • Often preceded by CA fuming for adhesion improvement.

Metallic Powders

  • Fine metal (usually aluminium) particles; light grey.
  • Applied with fibreglass brush.
  • May struggle on greasy plastics; ideal for highly polished silver, nickel, chrome.

Magnetic Powders

  • Iron grit + aluminium/copper flakes; applied via magnetic wand (no bristles).
  • Good for shiny magazine covers, ceramics, coated boxes.
  • Ineffective on magnetic surfaces.

Cyanoacrylate Fuming *

  • Heated glue + humidity inside chamber; water source and controlled temp.
  • Glue polymerizes on print residue, “fixing” fragile ridges (white deposit).
  • Fuming time ≈ 12 min; over-fuming fills detail.
  • Compatible with subsequent powdering or fluorescent dye stains.
Fuming Chamber Practice
  • Suspend items or place on racks; apply a few glue drops to heated dish.
  • Incorporate water to regulate humidity.
  • Variety of commercial chambers available.

Fluorescent Dyes (Post-CA)

  • Common reagents: Rhodamine 6G, Ardrox, Basic Yellow, MBD.
  • Multi-step protocols: dye application, rinse, ALS visualization.
  • Provide high contrast against CA polymer for photography.

Sticky-Side/Tape Processing

  • Dedicated “Sticky Side” powder ideal for adhesive surfaces (e.g., duct tape used to bind victims).
  • Consider potential DNA on tapes from face/mouth—coordinate with biology unit before destructive steps.

Documentation Best Practices

  • BEFORE processing:
    • Record chain-of-custody status (sealed? who submitted?).
    • Describe item (size, colour, wet/dry, visible prints, damage).
    • White-light + ALS search; photograph any patent prints (example slide showed visible print pre-processing).
  • DURING processing:
    • Log every reagent, time, temperature, concentration, order.
    • Photograph at each successful development stage.
    • Note negative or positive results for each attempt.
  • AFTER processing:
    • Decide on further steps (dyes, alternate powders) and document.
    • Progress to AFIS entry, manual comparison, and elimination print checks when appropriate.

Exhibit Retention & Disposal

  • Distinguish destructive vs. non-destructive methods when requesting processing consent.
  • Maintain chain of custody through detailed notes and seals.
  • Court usually accepts photographs; physical exhibits not always retained unless small (lift cards, paper fragments).
  • Personal property returned via investigating officer; schedule disposal accordingly.