Current Affairs Journal: Sixth Entry

Just recently I have uncovered another misbelief about forensic sciences. I guess all of you, like me, thought that fingerprints are foolproof and that there is no chance that fingerprints can belong to more than one person? Well, at least half of that statement is wrong. Fingerprints can indeed only belong to one person and one person only. Even identical twins don’t have matching fingerprints. But in forensic sciences, using fingerprints as identification has been doubted and questioned recently. The reason for that is (even though fingerprinting is considered highly reliable) that the methods of comparing fingerprints is „lacking objective standards“.
When fingerprints are analysed  there are two  certain aspects which are observed to distinguish the prints: Friction ridge patterns and minutiae points. The main focus in a forensic analysis lies on the minutiae points. The three patterns that can be found in any fingerprint are loops, arches and whorls. With a rate of 60%, the loop is the most commonly found pattern of the three. Minutiae points are certain features of the ridges on your fingers. About 9 different minutiae points can be distinguished and among these, the most common ones a bifurcation, a short ridge or a ridge ending. 

Now according to these points, fingerprints are compared. In order to be able to match a fingerprint to another fingerprint, a certain number of minutiae points must be matched. And this is where the problem lies: There is no fixed number of matched minutiae points, which makes a match a valid match. How do we know that a match of 5 minutiae points is a “real” match? And if you have two people that share the same 5 minutiae points, how likely is it that something like that occurs?
 The decision is entirely up to the examiner! Experts often declare something a match with about 12 or 20 matched minutiae points. Still, like I already mentioned previously, most of the time the decision is up to the examiner or the individual standards of the different labs.

Also, there are some flaws to the system that searches for matching fingerprints. A false positive, a fingerprint match which turns about to be “false”, and a false negative can still create an invalid evidence. A study conducted by Bradford T. Ulery, R. Austin Hicklin, JoAnn Buscaglia and Maria Antonia Robert, though, showed that only about 0.1% of all the examined latent prints in their study turned out to be a false positive. False negatives ( a print which is said not to be a match but actually is) are much more common with a rate of 7.5%. Even though the rate for both false negatives and false positives is quite low the number of errors that could, or do occur, is still immense.