Module 2: Fingerprints

Overview of Fingerprint Patterns and Identification

  • Focus of this section is on fingerprints, specifically patterns and identification points.

  • Purpose: Introduce important forensic disciplines and techniques to enhance evidence recognition.

Fingerprint Classification

Classification Fundamentals

  • A delta is defined as: a location in a fingerprint where two lines diverge forming a triangle.

  • Importance of deltas in fingerprint classification.

  • Three major classes of fingerprint patterns: based on their delta presence.

Classes of Fingerprints

  1. Arches

    • Fingerprints without deltas.

    • Represent approximately 5% of the population.

  2. Loops

    • Contain one delta.

    • Displays entry and exit from the same side.

    • Types of loops:

      • Ulnar Loops: Enter and exit toward the left little finger (ulnar bone).

      • Radial Loops: Enter and exit toward the right thumb (radial bone).

    • Loops constitute about 65% of fingerprints.

  3. Whorls

    • Contain two or more deltas.

    • Represent about 35% of the population.

    • Types of whorls include:

      • Plain Whorl: Inner area forms a complete circuit touching both deltas.

      • Central Pocket Loop: Pattern that does not touch ridgelines between deltas.

      • Double Loop Whorl: Comprises two distinct loop formations with their deltas.

      • Accidental Whorl: Contains various patterns, sometimes combining loops, whorls, or arches.

Special Patterns

Arches

  • Most arches lack deltas.

  • Tented Arches: Have deltas; characterized by rapidly falling and rising ridgelines.

Composition of Fingerprints

  • Fingerprints are approximately 98% water; the remaining 2% consists of grease, oil, salts, and amino acids.

Types of Fingerprints

  1. Latent Prints

    • Described as invisible prints from normal body secretions.

  2. Patent Prints

    • Caused by visible contaminants (e.g., blood, oil).

  3. Plastic Prints

    • Impressions made on soft surfaces (e.g., wax, butter).

Fingerprint Recovery Techniques

  • Techniques depend on surface type: porous vs. non-porous, smooth vs. rough.

  • On-scene techniques offer a limited fraction of available recovery methods compared to lab techniques.

  • Importance of lab work for comprehensive recovery of fingerprint evidence.

  • Avoid rushing to forego lab examination for immediate on-scene techniques.

Endurance of Fingerprints

  • Fingerprints can endure despite disturbances in the crime scene.

  • Important to attempt recovery despite evidence being seemingly ruined by other actions (e.g., investigator interference).

  • Advancements in fingerprint technology enhance the recovery of latent prints in difficult situations.

ACE-V Methodology

  • ACEV stands for:

    1. Analysis: Assessing a print for comparison.

    2. Comparison: Analyst views known and suspect prints side by side to assess minutiae.

    3. Evaluation: Deciding if prints match (identification/individualization) or differ (exclusion).

    4. Verification: A second examiner independently examines the prints to confirm conclusions.

  • Importance of verification due to increasing scrutiny of forensic methods.

Minutiae Characteristics

  • Comparison encompasses more than basic patterns (loops, whorls, arches); it includes distinct characteristics known as minutiae.

Types of Minutiae

  • Ridge endings: Lines that end abruptly.

  • Bifurcations: A single ridge splitting into two.

  • Lakes (enclosures): A ridge separates and rejoins.

  • Dots: Small ridge features.

  • Spurs: A bifurcation with a smaller branch ridge.

Variation in Fingerprint Impressions

  • Human skin elasticity means no two prints are identical; factors include:

    • Elasticity results in variations in details.

    • No standardized measurement criteria for matching minutiae; relies on examiner expertise.

  • Comparison yields points of similarity and dissimilarity.

  • Points of similarity lead to identification, while dissimilarities indicate no match.

Expert Opinions and Standards

  • No international standard for minimum points of identification; decisions are based on examiner judgment and training.

  • Possible outcomes of an examination:

    • Identification (match)

    • Exclusion (not a match)

    • Inconclusive results

  • Inconclusive comparisons may result from poor quality prints or environmental factors.

Evidence Collection Procedures

  • Photograph fingerprint evidence before any enhancements or lifting.

  • Strategic decision-making is crucial for evidence search: focus on areas where suspects might have interacted (points of entry/exit and relevant surfaces).

  • Consider characteristics of surfaces when selecting fingerprint recovery techniques:

    • Types of surfaces:

    • Porous (e.g., paper).

    • Non-porous (e.g., glass).

    • Smooth (e.g., varnished surfaces).

    • Rough (e.g., textured surfaces).

  • Acknowledge the need for conditions that permit evidence collection; if an item can be collected, prefer to do so for lab processing.

  • Proper preparation is essential, including aspect considerations like wet vs. dry surfaces and weather conditions at the scene.