Forensic Fingerprint Identification - Part II

Posted by Chris Morales on Mon, Sep 30, 2013 @ 12:05 PM

B. Latents

A latent fingerprint is an image of a finger left inadvertently under uncontrolled conditions, such as those related to a crime scene. The majority of latent prints lack sufficient detail or clarity to be used to identify someone. The following factors affect the quality of a latent for comparison and identification purposes:

Size: On average, a latent is one fifth the area of a rolled exemplar, thereby providing only a partial image of the overall pattern.

Absence of Focal Features: Many latent prints are missing the information-rich "core" and/or "deltas" (see §9.6), that enable the examiner to orient the print for comparison.

Contrast: When the contrast between ridges and grooves is poor, features are difficult to determine.

Pressure: Excessive downward pressure of a finger on a surface obliterates the detail of the friction ridge pattern while insufficient pressure fails to produce a useable image; lateral pressure produces distortion and smears the ridge pattern.

Dirt: Dirt can alter the appearance of ridge detail.

Patterned surfaces: Wood grains and other patterns inherent to a surface where a print is left can mimic and thereby obscure friction ridge pattens.

Irregular surfaces: Uneven surfaces produce images that distort the distance between the ridges and grooves in friction ridge skin

Overlaid prints: When prints under-or over-lie each other, isolating a specific latent’s pattern is difficult

Viscosity: The consistency of a substance, such as blood or oil, that produces a fingerprint image can distort the pattern of friction ridges

Processing Method: The procedure used to make the print more visible can distort the appearance of the details and ridge characteristics.

C. Levels of detail and Basic Patterns

As with toolmarks (see chap 11), three levels of detail are employed to describe a fingerprint. The first level is the overall pattern created by the flow of the ridges. There are three basic patterns: whorls, loops, and arches. A whorl is comprised of ridges that flow in a circle around the “core,” or approximate center, of the fingerprint. See FBI, The Science of Fingerprints: Classification and Uses, p 14 (Rev. 12-84 1985). Whorls are also distinguished by two “deltas,” or areas “where three ridge systems meet,” located below (toward the palm) and on each side of the core. Ashbaugh, Quantitative-Qualitative Friction Ridge Analysis: An Introduction to Basic and Advanced Ridgeology (1999). Loops consists of one or more ridges entering from one side of the fingerprint, then curving back and exiting out the same side from which they entered. Loops have one delta on the opposite side from where the ridges flow in and out. Arches are formed by ridges that enter from one side of the print and exit out the other with a rise at the center. Saferstein, Criminalistics: An Introduction to Forensic Science, Chap 16 (10th ed 2011). Sixty to sixty-five percent of the population have loops 30-35 percent have whorls, and roughly 5 percent have arches. Saferstein, Criminalistics, chap 16.

- Note: Some studies have indicated that different ethnic groups may have different proportions of Level I patterns. Swafford, Fingerprint Patterns: A study on the finger and Ethnicity Prioritized Order of Occurrence, 55(4) J Forensic Identification, 480 (2005)

The overall ridge patter impacts class characteristics to a fingerprint. Class characteristics are not sufficient for individualization to a specific donor finger.

-Note: In the late 1800s, in order to file and retrieve fingerprints for later comparison, Sir Edward Henry, an Englishman, created a classification system based on these three general patterns of friction ridges. See Saferstein, Criminalistics, chap 16. The Henry system provided the basis for early computer search systems (see §§9.24-9.25) and modified versions of it are still in use in some jurisdictions. More complex classification systems break down further the three basic fingerprint patterns into plain or tented arches, radial or ulnar loops and plain or accidental whorls and double loop and center pocket whorls.

Level 2 details, often referred to as Galton points after Francis Galton points after Francis Galton, one of the pioneers in the field of fingerprint comparison and identification, are found along individual ridges. These ridge details, also referred to as “ridge characteristics” or “minutiae,” consist of bifurcations (where the ridge splits in two like river forking), ridge endings (abrupt stops), enclosures or lakes (where the ridge-bifurcates and then rejoins itself), and single ridge segments known as “dots” or islands.” A fully rolled print, or exemplar (see §9.4), has on average 75-175 identifiable ridge characteristics. The type, number, and relative location of Level 2 details impart individuating characteristics to a print. Level 2 details are most commonly used to compare and individualize latent prints.

The third level of detail includes variations in ridge width and the location of pores. Most examiners look only to the overall pattern type poses. Considerable controversy surrounds the stability of Level 3 details (see Office of the Inspector General, A review of the FBI’s Handling of the Brandon Mayfield Case, Department of Justice Special Report (Mar. 2006), available at http://www.usdoj.gov/oig/special/s0601/PDF_list.htm), and examiners disagree whether the third level of detail should be considered. For more terms and concepts related to fingerprint comparison, see the Scientific Working Group on Friction Ridge Analysis, Study and Technology (SWGFAST) Glossary (May 2009), available online at htpp:/www.swgfast.org/documents/glossary/090508_Glossary_2.0.pdf.

A latent print may contain one, two, or three levels of detail depending on its clarity. The levels of detail may vary in different area within the print.

 The Morales Law firm would like to thank Scientific Evidence in California Criminal Cases for sharing this information with us

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