How are left and right fingerprints connected?


What is dactyloscopy?

Fingerprints are examined using the fingerprint method. The technical term for this is called dactyloscopy, which literally means "finger look" (from the Greek words "daktylos" = finger and "skopein" = look). Fingerprint experts evaluate, among other things, crime scene traces and are responsible for person recognition.

Fingerprints have established themselves as evidence in criminology because they are unique and unchangeable. They can also be divided into certain basic patterns.

The origin of dactyloscopy

Fingerprints have by far the longest history of all biometric recognition methods. As early as 1684, the British botanist Nehemia Grew published a work on fingerprints. In his investigations he described characteristic features such as skin grooves, furrows, valleys and pore structures.

In the 18th century, various researchers examined and described the anatomical formations of fingerprints. Scientifically, however, little importance was attached to the fingerprint.

In 1888 the natural scientist and geneticist Sir Francis Galton finally achieved the real breakthrough. Galton is generally considered to be the founder of dactyloscopy, i.e. the fingerprint process.

In an extensive study of fingerprints, he described the so-called minutia property of fingerprints for the first time. He showed that the characteristic lines - the papillary lines - in the fingertip are individually unique and inherited.

He was the first to grapple with the problem of individuality and found a way to mathematically prove how small the probability is that the fingerprints of two different people can be the same.

The basis for this was a model in which the fingerprint is divided into fields. On the basis of the individuality, i.e. the uniqueness of each individual field, Galton then calculated the individuality of an entire fingerprint.

Edward Henry made an important contribution to the identification and recognition of fingerprints in 1899. He and his two Indian assistants published the Henry system named after him. They classified fingerprints according to certain criteria and made it possible to compare different prints with one another.

The Development of Dactyloscopy

In the second half of the 19th century, fingerprinting became standard in India. The British colonial government struggled to distinguish the indigenous populations. This often led to friction in the distribution of wages and pensions and in health care. Fingerprint identification was a convenient and straightforward process.

The triumphant advance of the fingerprint in the 20th century led from colonial administrations to police authorities all over the world, to border stations and immigration offices.

In 1897, Scotland Yard found the first criminal on the basis of his fingerprints. Fingerprints as evidence in court were first admitted in Argentina in 1896 and in Great Britain in 1901.

How do fingerprint experts work?

Fingerprints must first be secured at the crime scene. The decisive factor is the material on which the prints are found. In the case of substances that have no absorbent properties, such as glass or plastic, the fingerprints can be made visible with soot powder and secured with an adhesive film.

It is more complex with paper or wood. This is where chemicals like ninhydrin are used. For safety reasons, however, the analysis then takes place in the laboratory.

In the next step, the fingerprints are identified on the basis of the so-called minutiae (lat. "Minutae" for "tiny things"), ie the outstanding features of a print that are unique to a person. Not an easy task, because the fingerprints at the crime scene are often incomplete, smeared or overlapping.

According to German law, the identification of a person is considered correct if twelve minutiae match between two fingerprints.

Since the beginning of 1994, the automatic finger identification system (AFIS) has been introduced to support the manual work of the experts, which enables the experts to use a computer to compare crime scene traces with existing fingerprints of criminals. And that nationwide.

The card index of the Federal Criminal Police Office contains more than 2.5 million fingerprints from criminals and from people who are in Germany in connection with an asylum procedure.

Criticism of the dactyloscopy

So far, no two people have ever been found with the same fingerprints. This finding is supported by the statistical calculations of the Briton Francis Galton. According to this, the probability that there are two people with identical fingerprints is 1 in 64 billion. Therefore, the proponents of dactyloscopy also firmly believe in the infallibility of its method. But there is increasing criticism.

In 1999, US lawyers first disputed the scientific nature of dactyloscopy and thus its informative value as evidence. The main concern here is the error rate in the evaluation. In order to convince the court of the reliability of the technology, the FBI carried out a test at the time and sent the fingerprints of a defendant to all laboratories in the United States.

The result was extremely embarrassing for the federal agency, as seven laboratories out of 50 could not establish an identity. In other test series in the USA, the error rate of the dactyloscopes was between three and 22 percent. That is clearly too high for a scientific process.

Correct assessment of fingerprints is therefore largely based on the experience of the respective expert. In 2002, a judge in the state of Pennsylvania ruled for the first time not to admit fingerprints as evidence.

In his reasoning, Judge Louis Pollak stated, among other things, that the comparison of properly taken fingerprints at the police station with latent fingerprints at the crime scene was unreliable. Because there are people who have very similar papillary patterns, so that the smallest imperfections can blur the differences in the print.

The sociologist Simon Cole from Cornell University in New York found in his study that the dactyloscopy has never been examined for its flaws. In any case, the ruling of the Federal Court of Justice of 1952 still applies in Germany, according to which the evidential value of the method is unreservedly recognized.