Science in court

Imagine the scene. Police are investigating a particularly brutal murder. A woman has been bludgeoned to death with a blunt instrument in an isolated farmhouse. There are no eyewitnesses, and no fingerprints. The murderer appears to have been wearing gloves.

But then forensic scientists strike lucky. A bloodstained jacket is found in bushes nearby, presumably discarded by the murderer. There are no obvious identifying marks - but a scientist runs his hand-held DNA profiler over the jacket. From sweat stains under the arms, he gets a hit.

On computer monitors back at the forensic science labs at Wetherby, details of the suspect flash up - his name, description, photo, address, distinguishing features - even his work telephone number. Within hours he's been arrested and charged.

Sounds like science fiction? For now, maybe. But Mike Barber, a DNA forensic specialist at Wetherby, says that as far as the future of forensic crime detection is concerned, the sky is the limit.

Already, DNA profiles can be successfully obtained from minute samples of blood, semen or hair recovered from a crime scene - even from saliva from a cigarette stub, bottle or glass.

New techniques are now being developed for the recovery of even more minute traces of DNA: skin cells left behind when a suspect touched a door handle, say, or traces of sweat from their hands. Such techniques could give a hit even if there was no viable fingerprint, Mike says - because the prints had smudged, or the material touched wasn't the kind that would carry prints.

Mike is among scores of white-coated scientists who work from the Wetherby Forensic Science Laboratory - one of six British labs which make up a service Mike proudly boasts is the world leader in DNA profiling. It's not only murder and rape cases they work on - staff at Wetherby helped identify victims of the Paddington rail disaster and the Branch Davidian mass suicide in Waco, Texas.

DNA profiling, of course, isn't the only technique they employ. Andy Hunt has been working on serious crime cases for 30 years - he helped in the search for multiple-killer Barry Prudhom back in the 1980s - and has often been the scientist on the ground at crime scenes.

DNA profiling is wonderful, he admits: but it's not everything. The wear on the sole of a shoe obvious from a footprint can often be just as useful.

"It can be conclusive," he said. "As soon as you start walking, you pick up marks on your shoe. No-one will have the same marks, because we all walk differently."

Andy says a crime scene is rich in potential clues: fibres from clothing, minute flakes of paint or wood, blood, semen or saliva samples - even stab marks on a murder victim's body which can give a good idea of whether the weapon used was a broad-handled knife or a pair of scissors.

Nothing must be missed - because scientists don't know when they first arrive what they are really looking for and what may prove to be important later on.

He says one useful technique is the 'taping' of a victim's body. The body is covered in strips of sticky tape which are then taken off - carrying with them evidence that might have been left on the body.

Any evidence recovered is then scrutinised in minute detail back at the laboratory. It may prove possible, for example, from traces of wood or soil, to show that an attack did not happen where the body was found, but somewhere else, and was later dumped.

Andy, in a sense, is a forensic scientist of the old school. And while his methods are still crucial, it's the rise of DNA profiling that probably points the way to the future. The relentless march of science means there may soon be nowhere for the criminal to hide.

At the moment, DNA profiling can only be used to match DNA with the profiles of known, convicted criminals held on computer databanks.

But, Mike says, by analysing DNA traces found at a crime scene scientists may soon be able to give police a description of a suspect - colour of eyes, skin colour and hence racial origin, height, even whether a suspect is fat or thin - even where there was no match on police computers.

While DNA profiling is now a lengthy, expensive process that can only be done in the laboratory, miniaturisation may one day make it possible to develop a hand-held profiler that could be taken to a crime scene and used to give a reading in ten minutes flat. But before we as a society plunge headlong into a brave new world of hi-tech crime detection there are some real concerns to be addressed.

Should we, for example, set up a national DNA database with a DNA profile of everybody in the country?

That would certainly help in solving crime - but would it be in the best interests of the rest of us?

Mike Barber admits it is a civil rights issue - one to be decided by politicians, not scientists. "But I don't see why, provided the data is kept and held in good hands, we should not go down that route."

Not everyone would agree. Quite apart from the civil liberties issue, there is also the question of just how reliable DNA profiling is. A recent File On Four investigation on BBC Radio 4 highlighted the case of a Parkinson's Disease sufferer from near Swindon who was arrested in connection with a 'cat' burglary that took place nearly 200 miles away in Bolton.

Forensic scientists from Birmingham said there was only a one in 37 million chance his DNA profile - held on file after he'd been given a police caution for fighting with his wife and daughter - did not match samples recovered from the crime scene.

Despite his protestation he could scarcely walk, let alone climb through a kitchen window, he was charged.

It was only seven months later that forensic scientists admitted following 'further forensic analysis' that he was not responsible for the burglary after all.

The case, says File On Four editor David Ross, raises a big question mark over the infallibility of DNA evidence.

File On Four itself concedes the criteria for a DNA 'match' have since been tightened to a probability of one in one billion rather than one in 37 million.

Forensic procedures - designed, among other things, to prevent contamination of DNA from the crime scene with that of scientists analysing it - are very rigorous. But scientists are, after all, only human.

Mike Barber admits mistakes can sometimes happen.

And when you think about it, it could be a nightmare to be on the receiving end of such a mistake.

PICTURE: A forensic expert at Wetherby checks out a training shoe for evidence