In the history of forensic medicine there has been two great milestones: Fingerprints and deoxyribonucleic acid, better known as DNA: The first being well recognised, the later being the unique "hereditary fingerprint" passed on from parent to offspring.

A human being is made up of 50 million human cells, however even this basic fact was not recognised until around 1665 when Robert Cooke started to experiment with early microscopes. In 1869 Swiss biochemist Friedrich Miescher managed to find the separate elements of cells including phosphorus, carbon and oxygen, setting science on the path to discovering nucleic acid. This was then found to have two parties: ribonucleic acid (RNA) and deoxyribonucleic acid (DNA). Only since 1984 has science been able to examine and fingerprint these acids.

The far more recognised fingerprint (as found on solid objects that are touched by human hands) was discovered by Henry Faulds in 1880. He wrote in the magazine Nature that "when bloody fingermarks leave impressions on clay, glass, etc., exist they may lead to the scientific identification of criminals." Sadly his writing was mostly ignored and over eight years later Jack the Ripper left fingerprints with complete impunity.

The first case of a criminal conviction arising from the use of fingerprints came in 1892 in Buenos Aires. Two young children had been killed and a young mother was found with superficial throat wounds. She told police that a neighbour had rushed from the scene and cut her, but the police were sceptical.

By chance Inspector Eduardo Alverez had read about fingerprints in a science magazine and used the technique to prove that she and, not the neighbour, had left a vital bloody palmprint on a door. She later confessed and was sentenced to life in prison.

Startled by this success Argentina started to regularly use this technique in criminal investigation, but Europe and the rest of the world was slow to catch up. The first case using fingerprint evidence was in France in 1903 and the first case in the UK came 1905.

The technique of finding fingerprints took a giant step forward with the use of a system called "vacuum metallisation", in which the target surface is placed in a container from which air is expelled, creating a vacuum. In this state any liquified glue or powder in the vacuum will settle over the entire covered surface, however it will be unevenly absorbed by the ridges of moisture that make up a fingerprint.

Today it is a myth that computers can make a fingerprint match. What computers can do, however, is bring up pairs of fingerprints in which there is a close match and a human expert can then make the final decision. A score of eight identical "forks, spurs and islands" is enough for a suspect to be become the prime suspect, but more is preferable for them to be used in court. Seventeen is said to be the "top match."

In Alec Jeffreys of Leicester University wrote a new chapter in science history when he created the DNA genetic fingerprint. In 1984 he found the that genetic information repeated itself along a structure that looked like a twisted ladder. He also found that every person's DNA was different with the exception of indetical twins.

A single DNA strand is made up of equal characteristic of both parents and can be used in paternity disputes, where it is far more certain than pure blood tests. It is also used in bone marrow transplant surgery, if the transplanted marrow is healthy and replicating then donor DNA will be abundant.

It can also be used in breeding programmes of rare animals. Here they check that the animals are not too closely related - which is known to produce weaker animals.

Rather in the haphazard manner of the first fingerprint evidence, Leicestershire police decided to test this DNA system out on a vicious double rape and murder they were investigating in 1987. Convinced that the murderer was local they sampled 5500 men from around the scene. To complicate the story the actual killer had ducked the tests by having a friend step in, but his friend was overheard boasting about it in a pub.

The case was famous not only for the bringing a guilty man to justice, but allowing another to go free. The police had another man in custody and were about to charge him with one of the murders...