(1) In recent years, DNA evidence has been used to free many prisoners who were convicted of crimes they did not commit. (2) Many of these prisoners were originally linked to their alleged crimes through the use of fingerprint evidence. (3) While fingerprint evidence can be useful in solving a crime, it is not as foolproof as some people think.
(4) Every individual in the world has a unique set of fingerprints, so it seems as though it should be a good tool for identification. (5) The problem arises in the difficulty of determining whether or not two sets of prints are an exact match. (6) For a set of fingerprints to be properly recorded, the fingers are inked and then rolled, one finger at a time, onto a flat surface. (7) Or else they are scanned into a machine that captures and stores each finger as a digital image. (8) Such properly recorded prints can be quickly analyzed by a computer, accurately identified, and matched with another set of properly recorded prints.

(9) Fingerprints found at a crime scene, however, are rarely clean and distinct. (10) A fingerprint at a crime scene frequently shows only about 20 percent of the whole fingertip. (11) And crime-scene prints are often distorted because they are on an uneven surface or, sometimes, have been covered in blood. (12) These partial prints are difficult to read. (13) A computer cannot make an accurate match from such a print.

(14) Therefore, it is up to fingerprint experts to compare the crime scene print with a properly recorded print. (15) A fingerprint expert must then determine, to the best of his or her ability, whether or not the prints match. (16) Frequently, the link between a crime-scene fingerprint and a particular individual is determined solely by the skill and judgment of the person attempting to make the match. (17) Far from being foolproof, the determination is an inexact and subjective decision.

Choose the number of the sentence that expresses the central point in the selection