Forensics Lesson 3.10: Fingerprints
Introduction to Fingerprints
Fingerprints have been recognized since ancient times, but their significance as individualized evidence was not understood until the 19th century.
Various methods for collecting and analyzing fingerprints have been developed for solving crimes.
Goals for the Lesson
Describe the history of fingerprint analysis and its acceptance in law.
Identify essential characteristics of fingerprints and their major types.
Explain how forensic techniques for collecting and submitting evidence for court admissibility have evolved.
Describe national automated fingerprint identification systems and local fingerprint expert practices for searching large databases.
Analyze and validate fingerprints as individual evidence.
Classify fingerprints as individual evidence.
Explain techniques for lifting and evaluating identifiable fingerprints (latent, plastic, patent).
Compare the three major fingerprint patterns: arches, loops, whorls.
Identify fingerprint minutiae including bifurcations, ending ridges, dots, short ridges, and enclosures.
Describe methods for collecting fingerprint data at crime scenes, including processes for making latent prints visible.
Explain steps of crime scene processing.
Identify evidence linking a crime to its victim or perpetrator.
Explain the significance of impression evidence in investigations.
Historical Background of Fingerprinting
Fingerprints have fascinated people since antiquity:
Impressions in clay dating back to Babylon.
In ancient China, inked fingerprints were used as signatures.
Major historical advances in fingerprint understanding:
1788: Johann Mayer discovered that friction ridge patterns on fingertips are unique to each individual.
1823: Jan Purkynĕ described nine distinct fingerprint patterns.
1877: William Herschel recorded that fingerprints do not change with age.
1888: Francis Galton and Edward Henry created a classification system based on three main patterns.
1892: Galton published the first book on fingerprinting, detailing characteristics and classifications.
1892: Juan Vucetich matched a bloody fingerprint to a suspect using Galton's system (first recorded use).
Acceptance in Legal Context
Early 20th century saw widespread fingerprint use:
New York City started fingerprinting civil service job applicants.
Notable cases include:
1902: UK burglar convicted based on fingerprint evidence.
1910: Thomas Jennings convicted in the first U.S. case using fingerprint evidence.
Legal acceptance has grown, with evidence establishing durability and uniqueness:
1999 U.S. v. Mitchell upheld fingerprints under the Daubert standard despite challenges.
Understanding Fingerprints
Definition: Fingerprints consist of unique patterns formed by friction ridges and grooves on fingertips.
Components:
Ridges: The raised areas (friction ridges).
Valleys: The lower parts (grooves).
Pores: Openings on ridges (sweat gland outlets).
Fingerprints are unique, emphasizing their importance as individualized evidence. Each finger may have a different pattern.
Key Principles of Fingerprints
Three Principles of Individualization:
Fingerprints are individualized: No two individuals share the same ridge pattern.
Fingerprints remain unchanged throughout a person's life.
Fingerprints possess basic, classifiable patterns.
Classifications of Fingerprints
Three Major Classes:
Loop: Ridges enter and exit from the same side.
Ulnar loop: Entry/exit toward the little finger.
Radial loop: Entry/exit toward the thumb.
Occurrence: ~65% of the population.
Whorl: Circular or spiral ridge pattern.
Further classifications: Plain, central pocket, double loop, accidental.
Occurrence: ~30% of the population.
Arch: Ridges enter on one side and exit on the opposite side.
Types: Plain, tented.
Occurrence: ~5% of the population.
The Henry Classification System
Purpose: To simplify print matching and storage.
Methodology: Assigning values based on the presence of whorls.
Each finger assigned a number; those without whorls receive a zero.
Top and bottom scores calculated to categorize prints.
Results in division of 10 print records into one of 1024 groups.
Minutiae of Fingerprints
Definition: Tiny ridge pattern characteristics essential for identifying fingerprints.
Types of minutiae include:
Core: Center of any pattern.
Delta: Triangular ridge where patterns diverge.
Bifurcation: Where one ridge splits into two.
Island: Ridge that briefly travels and ends.
Ridge ending (termination): The endpoint of a ridge line.
Unique arrangement and types of minutiae enhance the individuality of fingerprints.
Modern Fingerprint Identification
Utilization of multiple metrics for individualization:
Class, minutiae, ridge count (the number of ridge lines across a standardized length).
Diverse combinations almost guarantee unique fingerprints.
IAFIS: Integrated Automated Fingerprint Identification System.
A sophisticated system facilitating comparison of millions of digitized fingerprint records.
Software utilizes minutiae for matching and notifying potential matches (hits).
Verification by certified fingerprint examiners affirm connections between evidence and suspects.
Types of Fingerprints at Crime Scenes
Categories:
Visible Fingerprints: Clearly seen from contact with colored materials (blood, paint, ink).
Plastic Fingerprints: Impressions left in soft materials (wax, soap, dust).
Latent Fingerprints: Invisible prints from oil or sweat transfer.
Methods of Collecting Fingerprints
Lifting methods vary by surface type:
Non-absorbent surfaces can use powders or superglue fumes for visibility.
Absorbent surfaces require chemical development (e.g., silver nitrate).
Techniques to reveal latent fingerprints include:
Iodine fuming: Reacts with oils; quickly fades.
Ninhydrin: Humidity-driven chemical reaction with amino acids. Visible in 2 to 24 hours.
Cyanoacrylate: Superglue fumes react with prints on nonporous surfaces.
Fluorescent light: Identifies components of perspiration under specific laser light.
Fluorescent dyes: Dyes that emit light under UV light.
Preserving Fingerprint Evidence
After developing prints, preservation is crucial:
Photograph developed prints using special lighting for clarity.
Evidence can either be stored in evidence bags or gently lifted using adhesive techniques:
Adhesive tape or sheets can transfer prints to a contrasting surface.
Conclusion
Fingerprints exhibit unique patterns characteristic of individuals.
Utilization of various collection and analysis methods at crime scenes can yield valuable evidence linking suspects to crimes, utilizing modern technological advancements like computerized databases for efficiency and accuracy.
In 1892, Juan Vucetich made a significant contribution to the world of fingerprinting by being the first to record the use of matching a bloody fingerprint to a suspect. He utilized Francis Galton's classification system for this purpose.