Fingerprints

Question 1

How are fingerprints formed?

Answer 1

Under the skin, glands excrete salts, fats, amino acids, proteins and water. These are deposited on what we touch, and the pattern they leave is based on the friction ridges of our fingers (lines).

Question 2

What are the 3 principles of fingerprints?

Answer 2

1) Based on 100 years of experience, no 2 people have the same prints, including identical twins, as fingerprints are formed before birth in the womb.
2) Fingerprints do not change in a lifetime, and remain after death for some time. Even after shaving off first layer of skin, it will grow back the same way. It is possible to lose your fingerprint completely though
3) Patterns can be classfied

Question 3

What are latent fingerprints?

Answer 3

Fingerprints that are not visible to the naked eye and requires chemical visualisation

Question 4

What are 5 ways to chemically visualise fingerprints?

Answer 4

1) dusting powder: choose the colour that gives the most contrast against the background, and lift print on tape
2) visualisation reagents: ninhydrin, iodine spray, silver nitrate
3) laser fluorescence
4) fuming cyanocrylate: vapour from superglue, reacting with the chemicals in the fingerprints
5) infra-red microscopy: view fingerprints with infra-red microscrope

Question 5

How do fingerprint databases work?

Answer 5

Since we can classify fingerprints, we can use databases to give us close matches (but not perfect matches). Human judgement is still required