We spend a lot of our time in schools; we also work extensively with various community groups, individuals and businesses – talking about, and demonstrating, numerous forensic techniques. And one of the areas we discuss in detail is fingerprinting.

There are hundreds of ways to capture fingerprints at a crime scene, which are influenced by such things as the surface the fingerprint is on; the condition of the print; whether it’s a full or partial print; the surroundings and atmosphere (inside or outside, for example); and many other things.

But if someone is a non-secretor (non-secretors make up between 15% and 25% of the population), though they may leave some semblance of a fingerprint behind, there’s usually not enough DNA/information within it to identify the criminal. So, does this mean they could they get away with murder…?!

When we touch something, the fingerprints we leave are created from sweat we’ve secreted, as well as other acids/fluids from our bodies. You’ll probably know that every fingerprint is unique, even between identical twins.

The ridges – the loops, arches and whorls – on the ends of our fingers are formed in the womb, as the buds on our hands move through amniotic fluid. No two foetuses move in exactly the same way or direction over the crucial weeks when their fingerprints are forming.

Does that mean, therefore, that a non-secretor can get away with a crime? Is it impossible for our police forces to identify and nab almost a quarter of the world’s population, should they break the law?

Of course not. Because it’s not just the fluids we secrete that get left behind. At any given moment, you will leave parts of your body, and traces of your DNA, from wherever you sit or stand.

You’ll lose up to 100 hairs a day, and, as you talk, you expel saliva from your mouth. On top of that, a human sheds between 30,000 and 40,000 dead skin cells every minute. Believe us when we say, secretor or not, you will leave a bit of ‘you’ behind at a crime scene – and anywhere else you go. This is one of the main reasons crime scene investigators don their white suits, gloves, masks, and other protective gear at a crime scene. The last thing the investigation needs is the investigators’ hair, cells, and saliva confusing things.

To become a fingerprint ‘expert’, and so that your findings are admissable and respected in a court of law, a person has to study fingerprinting (such as the characteristics, anomalies and identification procedures) for at least five years. And don’t forget the hundreds of ways they can be captured; all this will be of relevance to the fingerprint expert who will be challenged on their findings during criminal trials. Forensic scientists, working in the relevant field, study the subject of DNA for a similar length of time, and with the same level of scrutiny.

The simple conclusion is: no one gets away with anything, when up against experts!

Thanks to thawats at freedigitalphotos.net for use of the image.