Detailed Notes on Fingerprint Processing

Fingerprint Processing

Chemicals

  • A few chemicals used in fingerprint processing include:
    • Ninhydrin
    • Ardrox
    • Ramm
    • Iodine fuming (less common now due to hazardous nature)
    • Cyanoacrylate ester (superglue), always used before other chemicals or powders
    • Rhodamine 6G
    • Amido Black
    • Leucocrystal violet

Powders

  • Types of fingerprint powders:
    • Black
    • Bi-chromatic
    • Magnetic (white, black, silver, gray)
    • Fluorescent powders (red, green, blue, orange)

Steps for Fingerprint Development

  • Porous Surfaces:
    • Examples: Paper, cardboard, untreated wood.
    • Latent prints are absorbed into the material.
    • Ninhydrin is effective for these surfaces.
  • Non-Porous Surfaces:
    • Examples: Plastic, glass, metal.
    • Use Cyanoacrylate ester (superglue) first.
    • Follow with powder and/or a chemical treatment.

Types of Prints

  • Patent Prints:
    • Visible to the unaided eye.
    • Examples: Greasy impressions on windows, prints in blood, paint, ink, mud, or dust.
    • Lighting is crucial for finding patent prints.
  • Latent Prints:
    • Hidden or unseen; require enhancement.
    • Chemicals or powders are needed to visualize the print.
  • Plastic Prints:
    • 3-dimensional impressions in pliable substrates.
    • Examples: Clay, putty, soft wax, melted plastic.
    • Photograph using side or oblique lighting to highlight the impression.

Deposition Factors

  • How fingerprints are left on a surface depends on various factors:
    • Conditions:
      • Pre-transfer: Condition of the person’s skin (age, gender, occupation, disease).
      • Transfer: Surface conditions, texture, surface area, surface shape, temperature, contaminants.
      • Post-transfer: Environmental conditions like temperature, humidity, wet or dry conditions.

Material Types and Processing Techniques

  • Porous Materials:
    • Absorbent materials such as paper, cardboard, and wood.
    • Fingerprints are absorbed into the item.
    • Amino acid techniques are useful.
  • Non-Porous Materials:
    • Repel moisture; examples include glass, metal, plastics, painted wood, rubber.
    • Fingerprints remain on the outermost surface.
    • Effective techniques: Cyanoacrylate, dye stains, powders, and vacuum metal deposition.

Processing Steps

  • Visual inspection with light or laser.
  • Sequential processing: Superglue, powder, chemical dye stain.
  • Ninhydrin is used for paper, cardboard, or wood.
  • Lift the print or photograph it.

Composition of Latent Prints

  • Sweat is a major component.
    • Skin is the largest organ in the body.
    • Functions of skin: Regulates body temperature, moisture retention, protection, sensation.
    • Two main layers: Epidermis and Dermis.

Epidermis

  • Composed of several layers:
    • Stratum Basale
    • Stratum Spinosum
    • Stratum Granulosum
    • Stratum Lucidum
    • Stratum Corneum

Dermis

  • Contains different connective tissues:
    • Collagen
    • Elastin fibers
    • Interfibrillar gel
  • Layers:
    • Papillary Dermis
    • Dermal Papillae
    • Reticular Dermis

Sweat Glands

  • Sudoriferous:
    • Eccrine
    • Apocrine
  • Sebaceous
    • Compounds either exude from pores onto friction ridges or are transferred through touch.

Eccrine Glands

  • Most common on palms and soles, but found all over the body.
  • Primarily for thermoregulation.
  • Function as a group, not individually.
  • Produce mostly water, but also organic compounds like amino acids.

Apocrine Glands

  • Associated with coarse hair in armpits and pubic area.
  • Produce a thicker fluid.

Sebaceous Glands

  • Small sac-like organs in the dermis layer.
  • Associated with body hair.
  • Found on the scalp, face, anus, nose, mouth, and outer ear.

Latent Print Composition

  • Approximately 99% of a latent print is water.
  • The remaining 1% consists of lipids and other organic compounds.

Ridge Development

  • 4th week: Fingers become visible; hand develops from paddle-like to hand form; volar pads appear.
  • 3rd month: Friction ridges begin to form at 10.5 weeks.
  • Volar pads regress, and friction ridges continue to grow until about 16 weeks, at which point minutiae are set.