Unit 195 Part A

16    We could tell whether the lights had been on at the time of the accident …
17    by examining the light bulb,
18    because there would be minute pieces of molten glass on the metal filament in the bulb.
19    Now, Sherlock Holmes might have found a strand of hair at the scene of a crime,
20    perhaps black and two inches long, that would have helped him identify the murderer
21    on the basis that the hair matched the murderer's.
22    Perhaps one person in twenty has black hair two inches long,
23    so we need to improve on this analysis to narrow down the number of suspects.
24    So, we would analyse the strand of hair, using the electron microscope,
25    as I was saying earlier, look at its chemical composition,
26    whether it came from a man or a woman, see how it was cut,
27    whether it showed any traces of particular chemicals and so on, and in that way,
28    instead of saying that one person in twenty had hair like that,
29    it might be one person in 500,000 or a million.
30    Now there's no such thing as certainty, just a balance of probability,
31    even with the most advanced techniques of genetic fingerprinting.
32    The evidence we provide is there to be interpreted, and that's very important.