Chapter 14 Fingerprints

Fundamental Principles: 1st principle No 2 prints are identical Determination of characteristics Calculations have been made over the years; statistically supported Not determined by general shape or pattern, but by study of its ridge characteristics (minutiae) Identity, #, and relative location of characteristics that give individual characteristics There are an average of 150 ridge characteristics on average fingerprint

1st Principle, cont. A whole print would be nice Here’s the debate In practice, many prints recovered are only partials How many ridge comparisons are necessary before 2 fingerprints can be identified as the same? Anywhere from 8-16 have been used. No statistics yet on the minimum # that is accepted

2nd Principle: Remain unchanged during lifetime What are fingerprints? What you see (print) Reproduction of friction skin ridges found on palm side of fingers and thumbs Natural purpose: provide our bodies w/ a firmer grasp & resistance to slippage Lines corresponding to hills (ridges) & valleys (grooves)

2nd principle Skin Epidermis – layer closest to skin Dermal papillae – layer under epidermis the shape of this boundary layer is what gives you your print Layer forms while developing as a fetus Don’t change, just enlarge as grow Dermis – inner layer; under papillae

2nd principle Skin, continued Each ridge has row of pores that lead to sweat glands Perspiration is discharged and deposited on surface When touch something, you leave the perspiration and oils behind that give the ridge impression These prints are invisible = latent prints

You don’t have to copy this one… It is IMPOSSIBLE to change your fingerprints, but it has been tried You would have to penetrate 1-2mm deep to get to the dermal papillae and eliminate all possible ridges, which is almost impossible You would also just create new ridge characteristics and permanent scars which could be used to ID

3rd Principle – RIDGE patterns allow for systematic classification 3 main classes Still look for the distinguishing characteristics Loops (60-65% of population) Whorls (30-35%) Arches (5%) Ridge characteristics – bifurcations, ridge endings, ridge crossings, enclosures, islands, short ridges, etc

3rd principle Loops Must have 1 or more ridges entering from 1 side of print, recurving to exit from same side Opens toward little finger = ulnar loop; opens toward the thump – radial loop Surrounded by 2 diverging ridges known as type lines All have 1 delta

3rd principle whorl All have type lines (2 diverging ridges) and at least 2 deltas Must have 1 section that makes a comple circuit Plain whorl, central pocket loop, double loop, accidental whorl

3rd principle arch Plain arches – ridges enter from one side and exit on opposite side, rise in center; forms a wavelike pattern Tented arch is similar except raised part in center is more of a spike Don’t have type lines, deltas, or cores