All in the genes, but taking DNA is also taking liberties

Published in Tribune, 14 September 2007

TWENTY years ago this week, Colin Pitchfork, a Leicester baker was arrested on suspicion of raping and murdering two 15-year-old girls. Analysis of a DNA sample taken from him while he was in police custody showed that it matched semen found on the victims’ bodies and, within months, he was in prison, serving two life sentences. Pitchfork was the first criminal ever to be convicted thanks to DNA evidence.

In the 20 years that followed his conviction, DNA fingerprinting has become cheap, relatively simple and a routine part of criminal investigations. (It has also mostly overcome technical pitfalls that landed several innocent people in jail when it was first used.)

Today, instead of investigators taking samples and carrying out mass testing on an ad hoc basis each time a violent crime is committed, like they did with the Leicester murders, the Home Office has a database, in which details of all the samples taken by the police are stored permanently. It's efficient, has caught many dangerous criminals, but should also give us cause for concern. It’s a powerful technology that has been put to use without safeguards for civil liberties.

Initially, it was a small exercise in keeping tabs on convicted violent criminals so as to easily identify if they were linked to further offences. But, since a change in the law in 2004, the DNA database has become a record of the genetic fingerprint of every single person arrested in Britain for any reason, whether or not they are charged, let alone convicted.

The database has grown to contain the details of more than four million British residents, around one in 15 of the population, more than the number who voted Labour in the last European elections. It’s a sample which is disproportionately made up of the young, the poor and ethnic minorities.

Given the extent to which the national DNA database has grown with barely a murmur of public concern, it was hardly a surprise that Stephen Sedley, an appeal court judge, suggested a few weeks ago that we should now put samples from everyone (including tourists visiting Britain) on the database.

But there is nothing inevitable about the implementation of this technology. Given its largely undocumented pitfalls, it is odd that Britain should have thrown itself so enthusiastically into it, and odder still that there hasn’t been any real debate. It’s perhaps in the nature of such complicated technical innovations – they always seem to inspire either irrational distrust or complete indifference.

Although DNA fingerprinting technology is very accurate, its use is inevitably less clear cut. The judgement of whether two samples (a suspect’s and one discovered at the crime scene) truly match is not a simple one, and relies on the skill and training of the forensic scientist analysing the samples as much as it does on the sophistication of the computer algorithms that search the database. Contamination (and falsification) of samples is always possible. False positives are rare, but not unheard of, and in the early history of DNA fingerprinting, African-Americans were notoriously prone to being wrongly fingered by DNA tests which were calibrated against white people’s genetic makeup.

But the real risk lies not in the technical pitfalls, which are minor (and receding as the technology matures), but in the way a positive result is used by the criminal justice system. Because a positive DNA match, as Kate and Gerry McCann insist, does not necessarily imply guilt. We shed hairs, sweat, saliva and even blood everywhere we go. Finding genetic material at a murder scene does not imply that it belongs to the murderer, it merely suggests that a person – or a piece of their clothing or any number of other things that can carry traces of genetic material on them – has been there at some time in the unspecified past, perhaps for an entirely innocent reason. And finding a murder victim's DNA on a suspect's belongings simply means that they came into contact.

But the legal framework that the British DNA database functions in cares little for these subtleties. It aims to cast the net of suspicion as widely as possible. Inevitably, even if charges rarely ensue, people whose DNA is on the system are more likely to be accused of serious crimes than those who are not.

So good luck to you if your head is picked out of the crowd and you don’t have an ironclad alibi. Lawyers often tell clients fingered by the DNA database to plead guilty, even when other evidence is woolly.

Juries, presented with the apparently black-and-white answers that DNA testing seems to throw up, rarely stop to look and see whether there are shades of grey. Is it right that we should subject people who have done nothing wrong to a lifetime of suspicion?

A less known fact about the Leicester murders is that some months before Pitchfork was arrested, the DNA evidence collected from the crime scene had actually exonerated the prime suspect, previously considered by the police as a dead cert for conviction. A vulnerable teenager, he had confessed to one of the murders under police interrogation – but the murderer’s DNA did not match his.

Genetic fingerprinting is a technology with the power to do a great deal of good when used with restraint and intelligence. But that Britain uses it so widely, and with so few safeguards, is a fact which ought to concern us all.