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18 November 2010

The science of deduction

Developments in the field of forensics should make crimes easier to solve. But a lack of funding thr

By John Naish

Wherever you go, you leave a host of hidden traces. In the coming decade, an array of new forensic techniques to detect and analyse them will become available. Investigators will be able to construct photo images of your likeness from a tiny sample of DNA; your hair will tell them where you’ve been; your unique “bacterial signature” will be used as a telltale fingerprint.

It may seem like the advent of a scientific surveillance society, but advances in forensic science are long overdue, say criminal justice experts. They warn that the basic standards of scientific courtroom evidence in the UK are failing to keep pace with demand. This is creating a double jeopardy, in which juries expect far too much from forensic evidence and forensic scientists often can’t make as much of DNA evidence as they might.

In the US, doubts about the reliability of forensic science have prompted a reassessment of forensic scientists’ ability to finger the guilty. The White House is formulating its response to a damning report on the state of US forensic science by an expert panel convened by the
National Academy of Sciences. The panel concluded in February last year that analysis of bite marks, blood splatters, handwriting and even fingerprints is not always backed by the kind of rigorous evidence expected in other scientific disciplines.

In Britain, similar qualms have been raised. According to Peter Gill, a senior lecturer at the University of Strathclyde in Glasgow, the science of DNA testing in Britain is failing to improve its levels of accuracy and reliability. Gill, a former analyst at the UK’s Forensic Science Service, warns that the government is not investing enough in developing the scientific interpretation of DNA samples so that these can be presented in court with increasingly clear evidence of how strong a match they make with anyone involved in a case.

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“The interpretation of DNA has undoubtedly been lagging behind other forensic research,” he tells me. “Big, sexy scientific breakthroughs are not really that important in court compared to being able accurately to identify a DNA profile that is partial and mixed with other samples. The latter is something that forensic scientists are having to do every day – but they are using the same methods that were being used ten years ago. Undoubtedly, that is leading to fewer DNA samples being used as evidence than should be possible.”

The CSI effect

Gill says that we could increase our forensic success rates – and our level of confidence in the science – if methods of statistically analysing and interpreting DNA were improved in ways that are transparent and testable by courts.

“But the funding for this kind of research is just not there,” he says. “We are in a strange position in Britain. The Home Office used to fund the research for the benefit of the country. Now, this has been made commercial. The providers in the UK are in competition. They want to make profits, so they won’t allow their methods to be open-sourced and freely available to anyone who wants to use them. That is the only way in which independent research can verify how accurate the systems are and that they are being used correctly – and that defendants can afford to use them in court.”

Yet while British standards of DNA analysis are lagging, juries’ expectations of forensics are soaring ever higher. Bernard Knight, formerly one of the UK’s chief pathologists and a lawyer, says that jurors’ weekly exposure to fantastical investigative coups on television dramas such as CSI: Crime Scene Investigation leads them to believe that science can provide impossible levels of certainty about guilt or innocence. Opening a new forensic training centre at Glamorgan University in March, he lamented: “Nowadays, we all feel that we’re experts on DNA, fingerprints and trace evidence and it’s causing a problem. Jurors expect more categorical proof than science will allow for.” According to the journal Forensic Science International, this problem has earned its own label in criminological circles – “the CSI effect”.

Meanwhile, technology is striving to realise many of these jurors’ improbable dreams. A group of researchers at Arizona University is working on gene-fit pictures that predict what a person looks like from their DNA sample. The team’s leader, the genetics professor Murray Brilliant, has studied the DNA blueprints of almost 1,000 people in relation to detailed measurements of their hair, skin and eye colour. Writing in the Journal of Forensic Sciences in February, he claimed to have found a relatively small number of DNA markers that cause most of the variations in skin, eye and hair pigment. With the exception of identical twins, no two people share a blueprint.

No escape

Even if criminals don’t leave DNA, it is almost impossible to avoid shedding “bacterial fingerprints”. A full 90 per cent of the cells in our bodies belong to microbes. The mixture of these bacteria is unique to each person and it is left whenever we touch a surface, say Rob Knight and Noah Fierer, microbiologists at the University of Colorado, in the journal Proceedings of the National Academy of Sciences. Comparing bacteria on computer keyboards with samples from the owners’ hands, they found that they matched closely enough to provide useful forensic evidence.

If your bacteria do not give you away, your diet might. A new technology under development called isotope ratio mass spectrometry could allow forensic investigators to work out from hair samples where individuals have been – because the ratio of isotopes of certain elements contained in food varies depending on where it was grown.

Revealing information could also come from the way you speak. Mobile phones are now commonly used to plan and execute crimes. Voices can be disguised with everything from false accents to synthesisers. But Volker Dellwo, a phonetic scientist formerly at University College London, has found that no matter how voices are disguised, they retain a rhythmic pattern that is idiosyncratic to the person, regardless of how fast they are speaking. The pattern cannot be detected by the naked ear, which makes it hard to disguise.

All these developments sound exciting but, for Gill, the real work lies in the fundamentals of DNA. “For the past couple of years, I have been trying to get funding from organisations such as the Economic and Social Research Council for work on improving DNA analysis. The message I get back is that the government should be funding this kind of thing. We are the only country in Europe that does not centrally fund forensic science,” he says.

Gill believes that it may take a tragedy for the state to begin tackling the problem. “Sadly, I don’t think this government will be interested in changing things. It’s got too many other things to worry about. It’s not until the wheels fall off the system – until there is a horrendous
miscarriage of justice – that this issue will get proper attention.”

John Naish

Animals to the rescue

Animal DNA offers another way to expose miscreants.

As any cat owner knows, cat fur sticks to everything. This creates a potential forensic trail from crime scene to perpetrator. Investigators at the University of California are establishing a feline DNA database to help speed up detection rates.

This kind of approach has already produced results. In Canada, Douglas Beamish is serving a 15-year sentence for murder after the fur of
a long-haired white cat was found stuck to a jacket that was discovered at the crime scene. It was genetically linked to the Beamish family cat, Snowball.

But the prize for the most innovative use of animals in forensics must go to the German police, who are pioneering the use of trained vultures to detect buried bodies. Sherlock, a five-year-old turkey vulture, is being trained by the Lower Saxony police force along with two hatchlings, Miss Marple and Watson, to locate fabric carrying the scent of dead people. Sniffer dogs can scour only 100 square metres per day at best. Vultures, according to Rainer Herrmann, a senior forensics officer, “can fly over many square kilometres. It would take the birds just a few hours to cover areas that would take dogs days.”

However, there is one potential disadvantage: the vultures are likely to start picking at the corpses that they find.
John Naish

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