When you look at someone you know, you generally might recognize them by something on their face. Eyes, hair and facial structure are ways we usually give descriptions of other people and how they recognize people we know fairly immediately. There are specific body attributes that we might use to describe a person, too. Things like height, weight, and body shape definitely play into recognize people. What you might not immediately think of when distinguishing people is fingerprints. However, as much as you might think it would be weird to walk up to your spouse and ask them to look at their fingers to make sure they’re really your spouse, fingerprints are something that are as unique to individual humans as our faces.
For the majority of us, fingerprints are taken when we get our driver’s license or ID. They are used as something to prove that you aren’t someone else, and always as a way to track that your exist. Others are fingerprinted when they are incarcerated or if they are subpoenaed as a reason for authorities to think they might be part of a crime. Either way, finger printing is an interesting tool that is has been used a lot in the past to identify people… but is it as accurate as it’s reputation?
To start, fingerprinting, more officially known as dactyloscopy, has been a tool that dates all the way back to the ancient Babylonians, but it’s been in use in the US since the 1858. Until DNA profiling came along in the mid 1980s, fingerprinting was considered the most reliable scientific data source that could help convict people of crimes. In the last 15 years, fingerprinting has come under fire though. There’s been a lot of debate about how precise the measurement and calculations are for fingerprinting and in the last 10 years there have been four different people who were once convicted on fingerprinting alone who have been exonerated based on new findings.
Let’s talk about how it works. For most of the time fingerprinting has been used in the US, it’s been done with ink and paper. Fingers would be pressed into ink and then on a card, either rolling the finger from edge to edge, or just keeping it flat. The card would then pick up the print on the card. Today, digital technology has replaced the analog ink and pen techniques. Fingers are pressed in silicon or a surface that scans the prints and they’re converted to a pattern of data that can digitally be stored and compared to other data patterns. Prints that come from crime scenes can come from everything from surfaces to objects to blood. The prints are then lifted with tape, special powders or digital readers and examined.
So what are the issues? Let’s review:
1. First off, there isn’t one worldwide database where fingerprints are stored. This is an issue when it comes to international crimes – crimes that are committed in one country that are committed by someone born in or living in another country. Say like a French defendant is on trial for a crime committed in France and fingerprinting is being used to connect them to a crime because their fingerprints were found at the crim scene. There are also a second and third set of prints that are not found in any French data base. It is possible that the other two fingerprints are either those of people who don’t have identification cards or driver’s licenses in France, or that the two fingerprints are that of someone who is not a French citizen. Fingerprints are not always double or triple checked with other agencies which makes it hard to use them as evidence for international crimes.
2. While technology is improving regarding accuracy of scanning fingerprints, they are still examined and compared to others using human pattern recognition. Just as eyewitnesses can misidentify people, objects and details, those who review fingerprints do not do so with 100% precision. Some experts in fingerprint identification even have different approaches in doing so which has led to debate in some cases where different experts have not agreed on who’s set of fingerprints they’re looking at.
3. Some people do not have fingerprints and or they have actually been known to slightly change. Some people’s ridges on their fingers are just not deep enough to get a great set of prints. Other times people who work manual labor, rock climb or have significant scars on the palms of their hands will have altered fingerprints depending on the day. These types of situations make it hard to get a good set of prints with ink and paper or via scanning. It’s then hard to identify people like this.
You might be thinking, what’s all this have to do with math? Well, fingerprints fall into three pattern types: loops, whorls and arches and the process of analyzing these, as well as ridge line patterns involves heavy calculation. We’ll throw out the formula that is used to express the probability of getting at least nnumber of matches between two sets of fingerprints. It’s this: P(X ≥ n) = P(Z ≥ (n−μ)) but we don’t want to focus on the technical stuff here, more just note that there are multiple ways using formulas and graphs that examine minutiae points that go down to a cellular level and it only gets more complicated from there. Thus, when experts look at sets of fingerprints, they are not examining them solely with their blind eye and noticing similarities. They are using measured statistical analysis heavy in math to form their opinions.
In the end, regardless of finger printing not always being 100% accurate, it transformed crime solving and forensics. While we might have more sophisticated tools, like DNA analysis now, dactyloscopy was math’s way of helping pave the way for a more calculated approach in helping solve crime… and all from the touch of our hands!
