Latent Prints: Hidden usually refers to prints recovered from crime scenes or evidentiary items

  • invincible friction ridge impressions of unknown origin

Patent Prints: Visible to the naked eye

  • recorded in blood, paint, grease, etc

  • Require chemical processing to improve contrast and photographed

Plastic Fingerprints: left in soft material

  • clay, glue, wax, etc

  • Ridges are visible but must be photographed for preservation

Matrix: what substance the latent print was left behind in

  • sweat or contaminants usually

Sweat is majority of the matrix that fingerprints are left behind in

  • eccrine sweat is the only sweat found in friction ridge skin

  • Eccrine sweat is 98% water, but also contains 22 amino acids

Sebaceous sweat comes from pores that contain hair follicles

  • composed of mostly lipids

Friction ridge impressions are generally left with a combination of eccrine and sebaceous sweat

  • why would sebaceous sweat be found in latent prints?

Most chemical reagents for developing friction ridges reac with lipids or amino acids

Substrate - surface the latent print was left on

  • Porous: absorbs gases or liquids (paper, cardboard, unfinished woods)

  • Non-porous: non-absorbent (glass, plastic, metal)

  • Semi-porous: can both resist and absorb (glossy cardboard, magazine covers)

  • Adhesive (tape)

Ideal Surface

  • flat and smooth

Non-ideal surface

  • fabric, round, small

Skin is elastic and three dimensional

  • latent prints are 2D and each time the finger is pressed onto a surface it can result in the image appearing differently

Causes of distortion

  • substrate (surface)

  • Matrix (what was the latent composed of?Sweat, blood, etc)

  • Deposition pressure

    • Too much pressure can result in tonal reversal (ridges and furrows are switched)

  • Movement

  • Currently no scientific method to age fingerprints

  • Sometimes latent prints can be dated indirectly because of the matrix they are deposited in

  • When possible, DNA should be collected prior to latent prints processing

  • Sometimes a decision should be made by requestor if DNA or latent prints evidence is more important

  • Sometimes latent prints may need to capture a photograph of a patent print/impression prior to DNA swabbing

    • Extra precautions are generally taken to avoid DNA contamination of the evidence by the latent print examiner

  • Condition of the substrate (texture and premeability)

  • Environmental effects (rain, wind, dry climate, humid climate)

  • Quantity of latent print material deposited

  • Method of development, documentation, and collection

  • Latent prints are 98% water, lipids, amino acid, and proteins, and environmental contaminants

  • As water evaporates the latent print can lose 98% it’s original weight within 72h of deposition