The best evidence, it is said, is a suspect caught red (handed, obviously).
Chances are there isn’t going to be an officer who just happens upon a burglar climbing out of that ground floor window every time (although it does happen every now and then). So it falls to us as budding forensic scientists and secondary investigators to gather the crucial evidence instead. Fortunately, modern scientific methods have made our job a little easier to catch suspects red- (or yellow, as you’ll see) handed after the fact.
First, a short history lesson: the grandfather of modern forensics is Dr Edmond Locard (1877 – 1966), who developed what has come to be known as Locard’s Exchange Principle. Dr Locard basically stated that every perpetrator of a crime will bring something into the scene, and take something away from it. Whatever the suspect touches, either on purpose or inadvertently, will be left with trace material — and conversely, the suspect will come away with some trace material from that object. The task of modern forensics is to find it, and this helps us catch the criminal — virtually red handed.
Although there are many ways in which trace evidence can be gathered, here’s a quick look at three simple ways to catch a suspect red handed: gun-shot residue, chemical tagging and of course, fingerprinting.
1. Sticky fingers leave the best imprints.
Fingerprinting is by far the most well known, and perhaps oldest technique we forensic scientists use, dating from the 19th century. The science and application of fingerprinting is now quite refined, and at the same time, startlingly complex. Put simply, our fingerprints, the impressions made by the surfaces of our fingers and toes, are unique to us. So, if we can find unexplained fingerprints at a crime scene, chances are good that they belong to our criminal — and this is excellent evidence. There are several types of fingerprint – but the ones we would probably be most interested in are called latent prints (or ones that are usually invisible to the naked eye and require development with some other medium) to establish contrast, make them visible and enable a mark to be lifted.
Each time a criminal comes in to custody, at least within England and Wales, their fingerprints are taken via an electronic machine. These are transmitted to a central, national database. If fingerprints are taken from a crime scene or a seized object, they can be compared to this database electronically. If there is a match – bingo – we have a suspect for our offence. They’ve been caught red handed! It’s a brilliant bit of trace evidence, which enables officers to make an arrest. This doesn’t prove the offence however, but at the very least, the suspects implicated will have to at least account for their presence at the crime scene.
2. Every bullet fired leaves something behind.
Gunshot Residue (GSR): it consists of particles of the explosive primer and components of the discharged part of the gun that explode when fired. In much the same way that explosives residue will coat any surface near the blast, GSR will coat the person pulling the trigger, as well as surrounding objects and individuals. Forensic analysis of GSR is, as you can imagine, really very good. Swabs of the suspect’s hands and clothing can be taken to examine it for GSR and is particularly valuable evidence if the weapon, or bullet fired is also recovered. GSR provides compelling evidence, particularly if found in high concentrations.
3. Tag, you’re caught.
What better way than to tag your suspects (yellow-handed)? Chemical tagging usually consists of a liquid containing a molecular code which can be “read” under ultraviolet light. Through a registering process, the code can be linked back to a particular owner or property. If an unsuspecting thief touches the invisible fluid, they are stained with it — and it doesn’t wash off. Once under the UV lights in custody, the fluid shows up if present. In that case, it is game over: swabs can be taken and linked to the crime scene. This fluid typically glows bright yellow under UV light and makes your suspects appear yellow-handed. There are some disadvantages to this solution: it’s expensive and it does wear off after some time.
Your Turn: Think we’ve missed a trick here? Know another fantastic way to catch a suspect by the hand and link them directly to a scene? Let us know in the comments, like always. We’d love to hear from you.