How Forensic Investigators Classify Fingerprints

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Fingerprints are classified by their ridge flow patterns: loop, arch and whorl. The ridge flow patterns are class characteristics. An individual cannot be identified by a fingerprint patterns, the individual can be lumped into a category.

If a latent print has one of the three general pattern types (arches, loops and whorls), any inked print not having that pattern is quickly removed from future comparisons against that print. While not all latent prints will have pattern types, most will have some general ridge flow that also can be used as a class characteristic. This ridge flow is also useful in determining from what skin area the print originated. Each area of ridges on the fingers have customary ridge flows that are characteristic of their location. A good example of this would be the delta region of a print. After determining the proper skin area, the pattern, or ridge flow, can be further utilized to orient the evidence in alignment with the inked print you are comparing it to.

After the class characteristics have been used to narrow the search to the correct print area, and the evidence print has been oriented, the examiner will select a reference point, with which to begin the comparison.

This starting point will frequently be at the core. A comparison of the individual characteristics, is then initiated. First, the examiner selects an individual characteristic within the evidence print, and then locates the same characteristic on the inked print.

When reexamining the evidence print, the examiner will then follow that ridge until a deviation of path or another unique feature is located. These features may be a bifurcation of the ridge, an ending ridge, a dot, a short ridge, a notable feature along the edge of the ridge, or distinctive pores atop the ridge. The comparison phase will continue until the entire evidence print has been compared, or until sufficient area has been examined to support a definitive conclusion.

Fingerprint identification is a complex topic, but is important for the forensic nurse to be abreast to what an investigator is looking for in a fingerprint.

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