Dactyloscopy – the art of fingerprint analysis


by Hiya Islam


You leave behind fingerprints everywhere, whether you like it or not. That’s not an issue when everyone else is doing the same. However, when found in a crime scene, things can turn nasty. This drags us to dactyloscopy, a method to study and compare fingerprints. Used in forensics, the goal of dactyloscopy is to establish identities of suspected individuals. But before we dive into some fun details, let’s take some time to appreciate fingerprints.

Our fingers leave their marks because of the sweat and oil on the ridges, produced by sweat glands underneath. At first sight, a fingerprint looks like a mess of lines heading nowhere. Closer observation will reveal that it consists of loops, whorls and arches only. As unique as it is, your print is very unlikely to match with another human. In case they do, you are 1 in 64 billion, the probability of a match. Even identical twins have unidentical prints! The current world population is at about 7.6 billion as of January 2018 according to Worldometers. Chances are slim, really. The extent of variety gets mind-boggling as studies reveal that each finger has its own pattern. Once formed in the womb, these do not change over a lifetime normally.

Therefore, what makes fingerprints invaluable in crime scene investigations is their uniqueness and permanence. Patent fingerprints are easily visible by the naked eye due to presence of blood, ink or dirt etc. in hands. Pictures of these are taken using high-end cameras with a built-in forensic measurement scale for reference. Latent prints are, however, difficult to detect and are the ones lying ‘everywhere’. How the prints can be lifted depends on the surface texture: smooth or rough, dry or wet, porous or non-porous and so on. And there are several ways to do it. First way is cyanoacrylate (superglue) fuming, where a non-porous object is placed in a specially designed chamber and exposed to superglue flames. The vapor will stick onto any print that is present which can be viewed under an appropriate light source. The second technique involves the use of fingerprint powder. The tip of a brush is dipped in the powder and the surface of the object is carefully dusted. Again, the powder will stick to the oil in the print. Pictures are taken of the now-visible print. Using a clear adhesive tape, the print is lifted. The tape is stuck to a lift card for preservation of the print. Thirdly, chemical developers are sought after when it comes to porous materials like paper and cardboard. Ninhydrin, also used in paper chromatography, react with the components in the residue to give a purple colour. DFO or 1,2-diazafluoren-9-one, when added to surfaces causes fingerprints to fluoresce under blue-green light.

Once the fingerprints are successfully collected, it is the job of fingerprint examiners to reach a conclusion. They use ACE-V (analysis, comparison, evaluation and verification) method. At first, it is analysed if the print is suitable enough for a comparison. Comparison is made using known fingerprints from databases. Then, the analyst evaluates his findings to see if there is a match or none. Lastly, another examiner repeats the same process to support or disprove the results.


Hiya Islam is a student of BRAC University.





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