Fingerprint Evidence

Fingerprint evidence is crucial in forensic science as it provides unique identification for individuals, making it an essential tool in criminal investigations. By analyzing the unique patterns and ridges present in fingerprints, forensic experts can link suspects to crime scenes or determine the identity of unknown individuals.

History of Fingerprints

  • fingerprints are amongst the oldest an most probative types of forensic evidence

  • Nehemiah Greew (1641-1712): first documented person to study and accurately describe ridge patterns on the surface of the hands and feet

  • Alphonse Bertillon (1853-1914): his system was called anthropometry

    • anthropometry- a series of 11 body measurements of the bony parts of the body, and an in-depth description of marks on the surface of the body

  • Will West shows anthropometric measurements were unreliable

  • Sir William J, Herschel (1833-1917): had workers sign legal documents by applying ink on the palms, and later thumb impressions onto documents

  • Henry Faulds (1843-1930): A Scottish physician who advocated for the use of fingerprints in criminal identification, recognizing their uniqueness and permanence.

  • Sir Francis Galton (1822- 1911): published the first recognized study of fingerprint science

  • Sir Edward Henry (1855-1931): trainee of Galton’s who developed a more functional classification system

  • Juan Vucetich (1855-1925): developed his own system called Vucetichissimo

What are Fingerprints

  • Skin is the largest and heaviest organ of the body

  • Volar skin is found on the soles of the feet, palms of the hand, and on the underside of the fingers and toes

  • Friction ridges on volar skin from patterns that do not appear in the smae place or sequences from one fingerprint hand, or toe to another

  • there are three kinds of sweat glands: eccrine, apocrine and sebaceous

  • A friction ridge is characterized by hills called ridges and balls called furrows

    • these ridges are called, arches, loops, and whorls

  • Subtypes of each pattern: ulnar/radial loops, plain/tented arches, plain/ central pocket/ double loop/accidental whorls

  • the ridges of fingerprints form the minutia or ridge characteristic by doing one of three things

    • ending abruptly (ending ridge)

    • splitting into two ridges (bifurcation)

    • forming ridge dots

Types of Fingerprints

  • Three distinct prints found at a crime scene are plastic, patent, and latent

  • Plastic: Fingerprints that come in contact with a sort of material (soap, wet putty, wet cement, wet paint, etc.) and have the impression

  • patent: easily identifiable as fingerprints by the unassisted eye

    • finger that has been in contact with a colored material (ink, blood, paint, oil, etc.)

  • latent: prints that require additional processing to be rendered visible

    • body perspiration and oils might leave invisible residue on surfaces

    • processing of latent prints in accomplished through development, enhancement, and visualization

Searching for and processing latent prints

  • Latent prints can be found on almost any type surface

    • latent prints will not be developed on every attempt

  • Fingerprints can evaporate if not processed in a timely manner

  • Once a print has been located, it must be documented with photography and then a processing method is determined

  • four primary methods to processing a fingerprint: physical, chemical, special illumination, and a combination approach

Methods

  • physical methods: utilizing the application of fine particles to the fingerprint residue

    • the most common physical method is powder dusting, or magnetic powder using

    • fingerprints on smooth, non-porous surfaces such as glass, paint, glossing plastics, etc. can be developed with powder

    • do not over dust because the print may be wiped clean

    • lift with fingerprint tape

  • Magnet powder is used on non-magnetic surfaces

    • an advantage of magnetic powder is that the powder only touches the print, so there is no possibility of damage to the print

    • small particle reagent (SPR) is another technique used

    • suspension of molybdenum sulfide grains in water and a detergent solution

    • can be used on wet/dry/greasy surfaces

  • chemical methods involve reactions taking place to enhance, develop or visualize a latent fingerprint

    • Ninhydrin and cyanascrcyate funding

    • Ninhydrin, an amino acid, reacts to form a blush-purple color

    • alternate light sources (ALSs) are light-emitting devices supplies with color filters that filter the source light so that the print can be viewed

Preserving and packaging latent prints

  • whether or not an investigator believes that the print is identifiable, the print should be properly processed, documented, and recovered

    • once the print is visible, it must be photographed

    • the print should then be lifted if possible

  • do not place items in plastic bags or allow them to rub against the side of packaging materials

Identifying fingerprints

  • prints many matches of certain points of comparison before an identification is considered a positive match

  • There is no definitive rule on how to achieve this comparison

  • Minutiae are compared, point by point

  • pore shape, locations, numbers, relationship, and the shape and size of edge creatures are compared

  • ID’s are always made by trained and often certified examiners, experts

Classification of Fingerprints

  • Classification: a formula given to complete a set of ten fingers as they appear on a fingerprint car generally based on pattern type, ridge count, or ridge tracing

  • FBI National Information Crime Information Center-fingerprint classification: and the Henry system are used to classify prints

    • Henry system was developed by Sir Edward Henry

    • required complete classification of all 10 finders of an individual

  • NCIC-FPC: assigns a 20-character string of letters and numbers to a person's fingerprints

ACE-V

  • ACE-V: scientific comparison of prints

  • Analysis: a study of questioned print to determine the overall print orientation, quality, shape, and ridge flow

    • If the known print and the questioned print are found to be consistent, then proceed to the next level

  • Comparison: orienting the questioned and known print in the same manner and identifying a common unique point in each print

    • being with the most distinctive feature identified and continuing until all of the characteristics are accounted for and there are not unexplainable variances

  • Evaluation: an ID can be made based upon the degree of ridge detail

  • verification: another examiner re-examines the print for verification utilizing

  • the same process

    • the examiner making the ID should be someone who is not associated with the case

Automated fingerprint identification system

  • AFIS: an automatic pattern recognition system that consists of three fundament stages

    • data acquisition: the fingerprint to be recognized is sensed

    • creature exreaction: a machine representation (pattern) is extracted from the sensed image

    • Decision making: The representation deprived of the sensed image is compared with a representation stored in the system

  • Ten-print cards are scanned into the system

    • they are run against current patent prints within the system of “unknown”

  • Computer assigns a percentage of probability on the matches generated

    • the final determination isleft up to the professionals, NOT the computer

    • Examiner must add or edit minutes