PATTERNS AND CLASSIFICATIONS
Every investigator should be familiar with the basic fingerprint pattern types to improve the quality of inked impressions taken for submission to identification bureaus. Fingerprints and major case prints taken for comparison with latent prints should always be as clear and complete as possible.
The basic characteristics in a fingerprint pattern are type lines, deltas, and the core. There are other finer points of distinction to be made in determining exactly what constitutes a particular pattern a trained classifier will use in classifying the print.
Fingerprint patterns have three basic classification designations. They are further classified into eight different types as follows:
Arches Loops Whorls
Plain, Tented Ulnar, Radial Plain, Central Pocket, Double Loop, Accidental
In plain arches, figure 16-5, view A, the ridges enter on one side of the impression and flow or tend to flow out the other side with a rise or wave in the center.
Figure 16-5.-Fingerprint patterns
Tented arches, figure 16-5, view B, are similar to plain arches with the exception that the ridges in the center form a definite angle; or one or more ridges at the center form an upthrust; or they approach the loop type, possessing two of the basic characteristics of the loop but lacking in the third.
A loop has one or more of the ridges enter on either side of the impression, recurve, touch or pass an imaginary line drawn from the delta to the core, and terminate, or tend to terminate, on or toward the same side of the impression from which the ridge or ridges entered.
The loop must have three essential characteristics-a sufficient recurve, and its continuance on the delta side until the imaginary line is reached; a delta; and a ridge count of at least one. The classifier divides loops into two types-ulnar and radial.
Ulnar loops, figure 16-5, view C, are those types of patterns in which the loops flow in the direction of the little fingers.
Radial loops, figure 16-5, view D, are those types of patterns in which the loops flow toward the thumbs.
Whorls are those types of patterns in which the ridges form concentric circles or spirals or some variant of this geometric form. They are divided into plain whorls, central pocket whorls, double loops, and accidental whorls.
A plain whorl, figure 16-6, view A, has two deltas and at least one ridge making a complete circuit, which may be spiral, oval, or any variant of the circle. An imaginary line drawn between the two deltas must touch or cross at least one of the recurving ridges within the pattern area.
Figure 16-6.-Fingerprint patterns.
The central pocket whorl, figure 16-6, view B, consists of one or more recurving ridges, or an obstruction at right angles to the inner line of flow, with two deltas between which an imaginary line would cut or touch no recurving ridge within the pattern area. The inner line of flow of a central pocket loop is determined by drawing an imaginary line between the inner delta and the center of the innermost recurve or looping ridge.
The double loop, figure 16-6, view C, consists of two separate loop formations, with two separate and distinct sets of shoulders and two deltas.
The accidental whorl, figure 16-6, view D, is a pattern with two or more deltas, and a combination of two or more different types of patterns exclusive of the plain arch. This classification also includes those exceedingly unusual patterns that may not be placed by definition into any other classes.
Classification and Identification
Classification is simply a method by which a set of fingerprints may be suitably filed and easily retrieved for future use. Many fingerprint cards may have the same classification. Classification and identification are two distinct concepts that have only a casual connection with one another. Few latent prints recovered at crime scenes are classifiable. The majority of latents are partial or fragmentary impressions.
Identification is qualitative and quantitative comparison of one friction ridge print with another. Identification may be effected with impressions of any area of friction skin and is established by the individual ridge characteristics and their relationship to one another.
Frequently, prints may appear similar, but upon examination prove to have been made by different fingers. Many prints may also appear dissimilar because of the pressure or the curvature of the receiving surface, but examination by a qualified fingerprint examiner may prove they were made by the same finger.
Positive identification or elimination of fingerprints should always be made by a trained and qualified fingerprint examiner.