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Examination Process

The Fingerprint Sourcebook - Chapter 9


National Institute of Justice

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Introduction

The purpose of an examination is to determine or exclude the source of a print.* This chapter will discuss a method used by examiners to determine a print's source by looking at and comparing the general ridge flow in two fingerprints, the sequences and configurations of ridge paths, and if needed, the sequences and configurations of morphological details of a particular ridge and nearby ridges. This chapter also addresses the philosophies of perception and decision-making that all fingerprint examiners need to understand before turning to the mechanics of a comparison.

Many authors (Seymour, 1913; Bridges, 1942; Osterburg; 1977; Stoney, 1985; Stoney and Thornton, 1986; and Hare, 2003) have sought to describe an examination method or thresholds of sufficiency for source determination [Olsen, 1983, pp 4–15; Stoney, 1985; 1986, pp 1187–1216; Hare, 2003, 700–706]. These explanations usually involve visual aids or physical tools that demonstrate a sequence or configuration of a number of points (e.g., details of ridge endings, bifurcations, and dots). Some of these involve the use of transparent grids, tracings, overlaid prints, pinholes through photographic enlargements of the specific points in the prints, or an enlarged chart documenting correspond ing points. These efforts attempt to (and in some instances do) help to illustrate portions of the examination process.

The examination method of analysis, comparison, evaluation, followed by verification (ACE-V) is the established method for perceiving detail in two prints and making decisions. A thorough understanding of the sufficiency threshold within the method is essential. Merely arriving at a predetermined, fixed mathematical quantity of some details of a friction ridge impression (i.e., point counting) is a simplistic and limited explanation for why two prints originated from the same unique and persistent source or originated from different unique and persistent sources.

There is much more to prints than the arrangement of Galton points. The examiner must use knowledge and understanding gained from training and experience to make judgments about the features of the sources and details in prints to reach a conclusion about the origin of the print in question.

Cognitive science explains the processes of perception, decision-making, and development of expertise. Research in cognitive science is helping to explain how experienced examiners differ from novices [Palmer, 1999; Busey and Vanderkolk, 2005]. A philosophy of how examiners can determine or exclude a source of a print must be established for an examination method to be effective. Examiners draw from many philosophies to develop a particular examination method.

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