LONDON In September 1987, Colin Pitchfork, a baker from central England, became the first criminal in the world to be caught by DNA evidence, for the rape and murder of two 15-year-old girls.
He was sentenced to life imprisonment the following January.
Twenty years on, analyzing DNA from blood, hair, saliva or semen at crime scenes is ubiquitous and has helped solve hundreds of thousands of crimes.
But the scale of the forensic revolution is causing unease in Britain, where the government is considering casting the DNA testing net wider by allowing police to take swabs from people committing minor crimes, like dropping litter.
The case of British toddler Madeleine McCann, who went missing in Portugal, has raised questions about modern reliance on DNA evidence after theories multiplied based on the partial results from trace amounts of biological evidence.
Alec Jeffreys, the genetics professor who invented DNA fingerprinting in 1984 and went on to help police crack the Pitchfork case, is justifiably proud of his discovery.
He has a blurry image of the first ever DNA fingerprint on the wall of his office at Leicester University in central England.
Yet he is worried. He fears society has failed to grasp the ethical issues of DNA collection, its potential for abuse and the limitations of genetic analysis.
"The legislation is lagging really rather seriously behind the use of the database," he said.
"I take the simple view that my genome is mine. Under some circumstances, I'll allow the state limited access. But prying into my DNA ...? I am wholly opposed to that."
The debate has reached a crossroads in Britain, where more than 6 percent of the population, or 4 million people, are on the national DNA database -- far more than anywhere else in the world.
The United States, home to the biggest database, has 5 million profiles for a population five times the size.
The size of the British collection, which is growing by 30,000 a month, reflects the fact that police powers to take DNA are wider in England and Wales than in any other country.
Under 2001 rules DNA can be taken without consent from any person arrested for a serious, or "recordable", crime and kept even if that individual turns out to be innocent. In Scotland, samples must be destroyed if there is no charge.
Two Englishmen cleared of crimes are challenging the rules at the European Court of Human Rights -- but the British authorities are talking of expanding, not reducing, sampling.
New government proposals would allow police to catalogue DNA from those arrested for "non-recordable" crimes, such as littering and minor traffic offences.
Fanning the flames, a senior judge last month called for genetic details of everyone living in Britain, and all those who visited the country, to be added to the national DNA database, in a move described by human rights group Liberty as "chilling".
Britain's leading ethical think-tank, the Nuffield Council on Bioethics, has demanded a change of tack.
It urged the government in September to scrap its plans for wider DNA collection and stop the authorities keeping the DNA of people found innocent, arguing police efforts would be better spent on gathering more DNA from crime scenes.
Britain's Home Office, however, says crime statistics show current practices are effective, with 8,000 samples found to match DNA from crime scenes out of a total of 200,000 "innocent" samples collected by the end of 2005.
"We must consider anything which frees up police time or improves the efficiency and effectiveness of police investigations," a spokeswoman said.
GeneWatch UK director Helen Wallace sees shades of an Orwellian "Big Brother" society in such talk, as government wields increasing power to track individuals or their relatives.
Critics also warn about discrimination and stigma, since DNA collection by police is skewed by social factors, with young black men, for example, significantly over-represented.
Such dilemmas will only be magnified by new techniques like familial searching -- hunting for relatives of criminals who have a similar genetic profile -- and DNA "identikits".
Building a usable identity from crime scene samples is not yet a reality, since scientists can so far pick out only gender, red hair and unreliable guides to eye and skin color. But research is advancing rapidly.
Jeffreys warns DNA will never be a magic wand, particularly when experts are working with only trace amounts of biological evidence, as in the vexed case of British four-year-old Madeleine McCann, who disappeared in Portugal in May.
Portuguese police named Madeleine's parents Kate and Gerry McCann as suspects after receiving partial results of forensic tests. The McCanns say they are innocent and are running a high-profile campaign to find their daughter, who they think was abducted.
"If you are removing DNA from just a few cells from the scene of crime, you have no idea whether those cells are necessarily relevant to the criminal act or not," Jeffreys said.
"DNA does not have the words 'innocent' or 'guilty' written in it."