Sci-High: Fingerprints

Fingerprints

Fingerprints - patterns produced by friction ridges on the palmar skin - are one of the longest-established types of forensic evidence, their use having been established in the late nineteenth century. No two complete prints from different fingers have ever been found to be identical.

The three basics types of fingerprint are the arch, the loop and the whorl. There are many sub-types. The rarest type is not the one that people usually expect – it is the arch which occurs in only about 5% of the population.

In practice latent fingerprints are the most common – invisible prints on a solid surface usually produced by deposits of sweat. Many chemicals are present in them including amino acids, glucose and peptides. Transferred prints are produced as a result of a substance such as blood, oil or ink being on the finger. Occasionally impressed prints can be found in soft materials.

Latent prints can be visualised and collected from crime scenes in a variety of ways depending mainly on the composition, texture and colour of the item bearing the fingerprint. Powders of various colours and types are applied, most often using magnetic or conventional brushes. Specialised reagents are also employed. One of the latest developments was the discovery that the cyanoacrylate fumes of superglue react with components of fingerprints to produce a visible white material useful for locating fingerprints on a dark, smooth surface.

A portable permanent copy of fingerprints is usually provided by lifting or taking photographs. Visible fingerprints can be photographed directly, latent prints after they have been visualised and impressed fingerprints usually using special lighting conditions.

The comparison and interpretation of fingerprints have undergone some significant changes in recent years as a result of digitisation and the use of databases. In the United Kingdom the National Automated Fingerprint Identification System (NAFIS) holds the prints of people convicted of crime and fingerprints from undetected crimes.

Automated computer systems are now widely employed to assist in identifications and enable initial comparisons of prints to be carried out very quickly. But an identification has to be the personal judgement of an expert independently verified by another expert. Fingerprints remain an area of forensic science where the professional practical skills and experience of the practitioner are very important.

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Can fingerprints be removed? It is better not to try. The American gangster John Dillinger burnt his fingerprints off with acid. But the pain was not worth it - they grew back.

In our events, students use modern methods for the location, identification and lifting of fingerprints in the context of a wider forensic investigation.