Grayce P. Storey
Fingerprints can tie a suspect to a crime scene. Dusting for fingerprints is a technique criminalists may use at a crime scene.
There are three principles that relate to fingerprinting. The first principle is that fingerprints are an individual characteristic. No two fingers have yet been found to have identical ridge characteristics. The acceptance of fingerprint evidence by the courts has always been predicated on the assumption that no two individuals have identical fingerprints. The individuality of a fingerprint is determined by a careful study of its ridge characteristics (minutiae) and not by its general shape or pattern. Second, fingerprints will remain the same during an individuals lifetime. Fingerprints are a reproduction of friction skin ridges on the palm side of the fingers and thumbs. These skin surfaces have been designed by nature to provide our bodies with a firmer grasp and a resistance to slippage. Skin is composed of layers of cells. The outer portion of skin is the epidermis, the inner skin is the dermis. Between the epidermis and dermis is the papillae, which is a boundary of cells separating the two. Each skin ridge is populated with a single row of pores for ducts leading from the sweat glands. Once the finger touches a surface, perspiration along with oils that may have been picked up by touching the hairy portions of the body which are then transferred onto that surface. The result is an impression of the finger’s ridge pattern. Prints deposited in this manner iare referred to as hidden fingerprints because they are invisible to the naked eye. Lastly, fingerprints can be systematically classified according to their general ridge patterns. All fingerprints are divided into three classes on the basis of their general pattern: loops, whorls, and arches. Sixty to sixty-five (60-65%) percent of the population has loops, 30-35% have whorls, and about 5% have arches. The above three classes form the basis for all the ten-finger classification systems presently in use.
A loop consists of one or more ridges entering from one side of the print, re-curving and exiting from the same side. When the loop opens toward the little finger, it is called an ulnar loop; if it opens toward the thumb, it is referred to as a radial loop. The pattern area of the loop is surrounded by two diverging ridges known as type-line divergence in known as the delta. The core is the approximate center of the pattern.
There are four distinct groups of whorls: plain whorl, central pocket loop, double loop and accidental whorl. All whorl patterns must have type lines and a minimum of two deltas. A plain whorl and the central pocket loop have at least one ridge that makes a complete circuit. This particular ridge may be in the form of a spiral oval or any variant of a circle.
Arches are the least common and are divided into two distinct groups: plain arches and tented arches. The plain arch is the simplest of all fingerprint patterns. It is formed by ridges entering from the side of the print and exiting on the opposite side. Generally, these ridges tend to rise in the center of the pattern, forming a wave-like pattern. There is a similarity between the tented arch and the plain arch. The exception is that the plain arch rises smoothly at the center. There is a sharp up thrust or the ridges meet an angle that is less that 90%. Arches do not have type lines, deltas or cores.
There are three kinds of crime scene prints: visible prints made by fingers touching a surface after the ridges have been in contact with colored material such as blood; plastic prints, which are ridge impressions left on a soft material such as soap or dust; and invisible prints or true latents made by impressions caused by the transfer of body perspiration or oil present on ridges to the surface of an object.