Fingerprint Identification
8
Of all physical evidence at crime scenes, fingerprints are the most readily understood by the general public. Everyone has fingerprints, everyone “knows” that fingerprints are unique, anyone can compare two “patterns” to see whether they match. Mind you not everyone knows that the science of fingerprinting is known as dactyloscopy! What are fingerprints? Every person has minute raised ridges of skin on the inside surfaces of their hands and fingers and on the bottom surfaces of their feet and toes, known as 'friction ridge skin'. The friction ridges provide a gripping surface ‐ in much the same way that the tread pattern of a car tyre does. Friction ridge skin is also the only skin on the body without hairs. So fingerprints are rather less glamorously known by forensic scientists as friction ridges. The sweat glands in the skin of your finger tips produce a water based oil solution that coats the ridges of your print. These ridges retain a portion of this solution such that when the finger makes contact with a surface, a residue is left behind which is a facsimile of your print. How do they differ? Friction ridges do not run evenly and unbroken across our fingers, hands, toes and feet. Rather, they display a number of characteristics known as patterns and minutiae. Patterns are large‐scale (macro) shapes in the print, while minutiae are much smaller details. Patterns are like blood groups – there are only a few basic types – and only allow quick discarding of “suspects” with the wrong group, while minutiae provide the uniqueness of fingerprints. Patterns The three basic pattern types are: 
arch – all the lines in the pattern comes in from one side and go out the other [60‐70% of patterns] 
whorl – at least one ridge forms a complete circle [25‐35%] 
loop – lines come in from one side, turn and return to the same side [5%] EXERCISE 1 (a) Classify the prints below by their pattern type. 8. Fingerprint Identification It is more than likely that a individual will have more than different pattern types on different digits. Minutiae The principal categories of minutiae are as follows: 
ridge ending ‐ a ridge that ends abruptly 
bifurcation ‐ a single ridge that divides into two ridges 
lake or enclosure ‐ a single ridge that bifurcates and reunites shortly afterwards to continue as a single ridge 
short ridge or island – ridge that commences, travels a short distance and then ends 
dot ‐ an independent ridge with approximately equal length and width 
spur ‐ a bifurcation with a short ridge branching off a longer ridge 
crossover ‐ a short ridge that runs between two parallel ridges Minutiae, and their relative location on the print, provide the means by which identifications are made: sufficient points of similarity (typically at least ten) are necessary to make a confident match. It is an area of expertise – a general forensic investigator would do no more than confirm that a print might or might not be a match! Introduction to Forensic Science 8.2