#7 - fingerprints

Historical Context

Portrait parlé

  • Definition: A detailed verbal description of a perpetrator's physical traits by an eyewitness.

Anthropometry

  • Developed by Alphonse Bertillon to identify individuals by measurements of body parts, introduced in 1883.

  • Key tenets of the Bertillon System:

    • The bone structure of humans remains fixed post-age 20.

    • Appropriate measurements can distinguish all humans.

    • Precise measurements can be easily obtained.

Bertillon's System Success

  • Within two years, identified 241 repeat offenders using his measurement approach.

  • Three main components:

    • Body measurements

    • Head measurements

    • Limb measurements

Body Measurements

  • Height: Standing, seated, and reach (fingertip to fingertip).

Head Measurements

  • Maximum Length: Front-to-rear measurement.

  • Breadth: General width metrics.

  • Bizygomatic Diameter: Width between the cheekbones.

Limb Measurements

  • Measurement details:

    • Length of left foot.

    • Length of left middle and little fingers.

    • Length of the left forearm (elbow to the tip of the middle finger).

Transition to Fingerprinting

Alphonse Bertillon (1853 – 1914)

  • Developed anthropometry system for uniquely identifying individuals.

  • Eventually replaced by fingerprinting in the early 1900s.

Evolution in Fingerprinting

Early Observations

  • 1788: J.C.A. Mayer observed that skin ridges on fingers are unique to each individual.

  • 1892: Francis Galton proposed a classification system (loops, arches, whorls) based on fingerprint anatomy.

    • Suggested the existence of 64 billion different fingerprints.

  • 1900: Sir Edward Richard Henry expanded Galton's system, still in use in the English-speaking world.

Criminal Investigation Milestones

  • Juan Vucetich (1891): Developed a classification system used in Spanish-speaking countries, pioneered real fingerprint usage in investigations.

Notable Case Study

  • 1903: Will West vs. William West case highlighted limitations of the Bertillon system, fingerprints differentiated identity despite physical similarities.

Fingerprint Characteristics

Individual Characteristics

  • No two fingerprints can be found identical in ridge patterns.

  • Fingerprint stability through an individual's lifespan, maintaining ridge patterns.

Fingerprint Structure

  • Skin composed of two layers: Epidermis and Dermis.

  • Ridges and grooves comprise the epidermal surface, with sweat pores dotting the ridges.

First Principle of Fingerprints

  1. Individuality: No two fingers have identical ridge patterns.

  2. Permanence: Fingerprints remain unchanged throughout a person’s life.

  3. Systematic Classification: General ridge patterns allow for systematic comparison.

Ridge Features

  • Importance of the details in fingerprint identification, known as minutiae.

Different Types of Fingerprint Patterns

Loops

  • Comprise 60-65% of fingerprints; must have one or more ridges entering from one side, recurving and exiting the same side.

Whorls

  • Constitute about 30% of fingerprints; must contain type lines and at least two deltas, subdivided into four groups: Accidental, Double Loop, Central Pocket Loop, and Plain.

Arches

  • Comprise about 5% of fingerprints; no deltas exist.

    • Plain Arch: Simpler, ridges enter from one side and exit opposite, with a wave-like formation.

    • Tented Arch: Sharp upthrust in the center instead of a smooth rise.

Unique Features of Fingerprints

Micro Features

  • Commonly recognized minutiae include bifurcations, ridge endings, and sweat glands.

  • Unique combinations of these features create a distinct fingerprint profile.

Automated Fingerprint Identification Systems (AFIS)

  • Developed in the 1970s for computerized fingerprint classification and retrieval.

  • Can process thousands of prints per second, with integrated systems housing over 50 million records.

Detection Methods

Fingerprint Visualization Techniques

  1. Powder Applications: For hard/non-absorbent surfaces.

  2. Chemical Methods: Include iodine fuming, ninhydrin, and super glue (cyanoacrylate) fuming, among others, to make latent prints visible.

Causing Reactions for Latent Prints

  • Iodine Fuming: Produces brown stains, requires immediate photography for permanence.

  • Ninhydrin Application: Reacts with amino acids forming a purple-blue print, favored chemical method.

  • Super Glue: Used primarily on nonporous surfaces, forming a white outline of prints through vaporization.

Summary of Fingerprint Patterns

  • Understanding deltas:

    • One delta for loops, multiple deltas for whorls, none for arches.

Case Studies

  • Example of fingerprint recovery and classification effectively leading to arrests in connection with burglary cases.

  • Importance of proper processing techniques and application of chemical visualization in crime scene investigations.