1. Chapter 14 Fingerprints

2. 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

5. 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

6. 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)

8. 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

9. 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

10. 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

12. 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

13. 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

15. 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

17. 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