Fingerprinting

Fingerprints Fingerprints are created because of the friction ridges (epidermal ridges) on our fingers. The friction ridges increase surface area for gripping objects. They also increase vibrations from contact with objects that better transmit to the sensory nerves. There are also friction ridges on our palms and feet that can be used for identification as well. Oils secreted from the skin gets left on the surfaces that the fingers touch.

Exemplar prints Known prints deliberately taken from the person under controlled conditions. Each finger is taken separately and rolled from nail to nail. A slap print is taken as well of the whole hand. These can be taken with ink or scanned.

Latent Prints Any accidental leaving of a print visible or invisible. May be visible but not obvious. Can use electronic or chemical means to reveal them. Could be left from skin oils, paint, blood, dust etc. Often these are only a portion of the print and may be smudged. Have less clarity than an exemplar. Error is inherent.

Patent prints Accidental prints that are obvious to the human eye. Prints left in drying paint, clay, or in blood. Can just be photographed and do not need to be lifted.

Plastic prints Prints that are left in a material that maintains the shape of the friction ridges. Not found often. Could be in wet clay, melted candle wax, thick grease, putty around windows. Usually has latent prints around them as well.

Significance It is clear from the sample size that no two people have the same prints. When all ten fingers are cataloged it makes it even less likely. Prints are very difficult to remove. People have tried to cover them up or burn or sand them off, but they usually are not completely destroyed. Besides classifying each of the major print types, more information is necessary for proof.

Print Classification There are three main print types, although there are variations on each one. These are loops, whorls, and arches.

Radial vs. Ulner Specifics for loops % of all prints are loops. Radial loops are loops that start on the thumb side of the finger. Ulnar loops start on the pinky side of the finger.

Arch Arches make up 5% of all fingerprints. Arches can be regular or tented.

Whorls Whorls make up 30 – 35% of all fingerprints. There are many variations of whorls as well.

Collecting Prints Prints can be collecting by dusting. When dusting, a very small amount of dust should be used and only lightly brushed over the surface. Can be exposed by chemical vapors collecting on the oils as well. Can be seen using other instruments and scans that can leave the fingerprint intact and allow removal of print for DNA analysis.

Classification