Not surprisingly, the police are seizing upon DNA-testing, and the possibilities it opens up, to aim for what would once have been unthinkable - a 100 per cent success rate in tracking down murderers and other perpetrators of violent crime. It was that belief that put DNA in the headlines for a further reason last week: the call by the head of the Police Superintendents' Association, Chief Superintendent Peter Gammon, for DNA samples to be taken from the entire population. He argued that having a unique profile on computer of 60 million people would dramatically cut crime by acting as a deterrent as well as helping the police identify thousands of offenders at the flick of a switch. And, far from dismissing the idea as ludicrous - or even impractical - the Home Office believes the idea is worthy of discussion.
Certainly there seems to be no limit to the power and possibilities of DNA. Within the next decade forensic scientists are expected to be able to give police a full description of a suspect, down to hair colour and nose size, within hours of analysing a single cell found at the scene of a crime. So where is the science of DNA-testing leading, and should we be fearful or reassured by recent advances?
DNA - Deoxyribonucleic acid - is a chemical found in virtually every cell in the body and carries genetic information which determines the physical characteristics of an individual. Except for identical twins, each person's DNA is unique. Forensic scientists look at specific areas of DNA which are known to vary widely between people.
At present the national DNA database, set up in April 1995, holds about 300,000 genetic profiles from known or suspected criminals and 31,000 samples from scenes of unsolved offences. There is a backlog of a further 113,000 samples waiting to be processed by the Forensic Science Service which runs the database on behalf of chief constables in England and Wales. Scotland has its own system.
New samples of suspects' blood, sperm, saliva, and hair flood into the FSS laboratories every day, and every week between 300 and 500 are found to match the genetic "fingerprints" already stored on the database. Testing has become so sensitive that the probabilities of a match between a suspect and a DNA sample being wrong can be up to one in 50 million - good enough to convince most juries.
Police forces can take samples from anyone suspected or convicted of a crime that is punishable with a jail sentence. The vast bulk of the current profiles are from three main areas - violent and sex crimes and burglary. Forces are gradually including other offences, with at least two starting to target car thieves. In addition, about 9,000 inmates, convicted of serious crimes such as sex offences, have also had their details placed on the register. With the police issuing more than 400,000 new criminal records each year the potential number of profiles that could be included in the database under the current rules could eventually rise to about 5 million.
The police are also increasingly turning to mass DNA-screening to track down or flush out criminals. For example, after a woman is raped, young men living nearby can be asked to give DNA for analysis. Mass testing was used in 61 cases up to December 1997 and has involved 19,000 samples from which 21 people have been caught.
FORENSIC scientists are working on several projects that are likely to revolutionise the current DNA system. One recent breakthrough was the ability to recover DNA from dead cells. The mitochondrial DNA contained in dead hair and bones does not degrade like chromosomal DNA currently obtained from living cells. It can also be recovered from faeces.
While this scientific technique is not as accurate as the current system - it can only give up to a one in a 1,000 match - it has helped provide vital clues in cases where only tiny amounts of DNA were available. In the case of Lin Russell and her daughter, Megan, murdered in Kent two years ago, the technique provided a possible profile of the killer after dead hair was recovered at the scene of the crime. A man has since been charged with the murders.
DNA can be obtained from tiny samples - as tiny as a single cell - making it increasingly possible to go back to unsolved crimes and re-examine the evidence. This has led to the police cross-checking links between 207 unsolved murders to try to establish whether there are several serial killers are at large. So far 21 possible clusters have been identified.
Improvements in analysis also enabled fresh tests to be carried out in the case of James Hanratty, the man hanged in 1962 for the "A6" murder. In an attempt to establish Hanratty's guilt, traces on underwear of one of the victims were tested against a DNA sample taken from his brother, although only a partial match was made.
Scientists are also working on predicting the physical characteristics of a suspect from their DNA. They can already indicate, in half of the cases, which people have ginger hair. This project is expected to lead to the identification of eye, hair, and skin colour and later facial characteristics, such as the size of someone's eyes and mouth. A joint study with West Midlands police successfully predicted the race of a small sample of suspects.
The equipment used to extract and analyse DNA is also getting smaller and faster. Hand-held monitors able to provide an instant profile at the scene of a crime are predicted for the near future.
NOT everyone is delighted at the prospect of the all-seeing, all-knowing new scientific method of tackling crime. Organisations such as Liberty, the civil rights group, have questioned whether DNA is as accurate as the scientists would have us believe. They are also concerned that courts are becoming blinded by science and will automatically equate "one in a million" chance with a guilty verdict, although the FSS has stressed that DNA must never be the sole evidence.
Which leaves us with the question, is the introduction of a national database containing every citizen's genetic fingerprints only a matter of time? On the practical level it seems unlikely - the police, who pay for the tests, cannot afford to analyse all the known criminals, let alone law-abiding folk. The Home Office has also indicated its concern over civil liberties, although future governments may sing a different tune if crime starts to rise.
Last week Liberty argued: "While a balance needs to be struck between individual privacy and law enforcement we believe that the proposal for a national database goes way beyond what is acceptable or necessary in a democratic society."
This view appears to be shared by Dr David Werrett, Director of Research and DNA Services at the FSS, who said: "I would not be a great fan of taking samples from everyone. There are serious civil rights involved. We don't take fingerprints from birth - it would be a very big step forward."
So while a national register containing everyone's DNA is not likely to happen in the foreseeable future. What is inevitable is that the current database will continue to grow and improve, which is bad news for criminals.