by Dr. Miranda Trojanowska

The Sheffield Scientist’ Forensics Corner with Dr. Miranda Trojanowska


Alphonse Bertillon was a French police officer unhappy with the methods used to identify the increasing number of captured criminals who had been arrested on a previous occasion when it had been done by just name or by photograph. In the 1880s, he set up an identification system based on physical measurements in order to identify criminals. Because Bertillon’s method was so new and controversial, he was not taken seriously so in order to prove himself, he was forced to develop his measurements in his spare time using criminals in prison.This Bertillon system consisted of record cards with physical measurements of heads, feet and other distinguishing body parts. Along with these measurements, Bertillon used photography, now known as a mugshot,
to complete this system of record. The system was known to have its flaws as it was mostly designed for men who had reached full physical maturity and had short hair.

Around the same time, Henry Faulds, a Scottish surgeon, realised that fingerprints were unique and could be used as a means of identifying individuals. He proposed a method to record them with printing ink, which is still in use today, if digital equipment is not available, and these fingerprints are then stored digitally on a database, where they can be accessed by the Police to catch criminals. The general fingerprint pattern is inherited, but it is the movement of amniotic fluid around a foetus that causes slight changes, altering the finer details, making each fingerprint unique. Identical twins do not have the same fingerprints. Fingerprints may be employed by the Police to identify individuals who have left their fingerprints at the scene of a crime, or to identify people who are incapacitated or deceased and are unable to identify themselves. Dennis Nilsen, a serial killer, was caught because one of his victims was identified by his fingerprints.

In Argentina in 1892, one of the first cases where fingerprinting was used to convict a person was recorded. Francisca Rojas was found in a house with neck injuries, whilst her two sons were found dead with their throats cut. Rojas accused a neighbour and at the crime scene, a bloody thumb mark was found on a door. When it was compared with Rojas’ prints, it was found to be identical with her right thumb. She then confessed to the murder of her sons.

Fingerprints can be erased permanently and this can be used by criminals to reduce their chance of conviction. Methods include burning the fingertips using acid, rubbing them with a pumice stone or altering them using plastic surgery. John Herbert Dillinger was an American gangster of the Great Depression. He led a group known as the “Dillinger Gang” which was accused of robbing banks and police stations. Dillinger burned his fingers with acid, but prints taken during a previous arrest showed that they were nearly identical, meaning he didn’t do a very good job of getting rid of them.