Editorial: Don't take liberties with DNA tests

Genetic fingerprinting is a crime-fighting tool that has been perfected - as far as these things can be - within the past 10 years. We are still coming to terms with it. When a teenage driver was pulled over in Quay St, Auckland, recently an officer told him his traffic offence would be ignored if he agreed then and there to give a DNA sample.

When the incident came to light this week, it proved by no means unique. Parents came forward with similar accounts of their teenage children being stopped for a minor offence and asked -coerced perhaps - to contribute to the national DNA database. An Auckland lawyer said it was common for his young clients in custody to be offered cigarettes for a DNA swab.

We might wonder in passing that the officer did not simply pick up the finished fag. Technology now enables DNA matches to be made from cigarette butts, drinking straws, bottle necks, cans and clothing as well as blood, saliva, semen and hair. It would seem hard to consume anything in custody that would not leave a useful trace.

Others might wonder what is wrong with offering a traffic offender the chance to escape a fine by contributing to the database. Surely a law-abiding person would welcome the chance to avoid a $400 fine. If you were not the type to commit a crime more serious than a traffic offence, what would you have to fear?

That question implies complete faith in the forensic use of DNA. The science may be close to infallible but the collection and cataloguing is susceptible to normal human error. An example came to light not long after DNA testing started to solve crimes that had been sometimes long unsolved in this country. In 1998 DNA matches made a man the suspect of two Wellington murders though he had been in Christchurch at the crucial time. An inquiry blamed the mismatch on "contamination" of samples during the early states of processing at the Environmental Science and Research laboratory in Mt Albert.

As the law stands, DNA can be compulsorily taken from people in prison and from suspects of violent or sexual crimes and burglary. The net has been steadily widened and there is constant pressure to extend it. The Police Association has told Parliament it believes officers should have the right to take samples from anyone arrested for a chargeable offence.

The police want to take DNA samples from their recruits after fingerprinting pinned a crime on one of them recently. And the Sensible Sentencing Trust has suggested compulsory DNA tests for those found guilty of hurting animals.

There were said to be exactly 62,638 samples on the national DNA database this week. About 10,000 are added each year.

That seems a modest tally for a technique that has become temptingly simple and supremely valuable in solving crime. It suggests that the cases that have come to light this week are not the tip of an iceberg, though they may have been the beginning of an unwelcome tendency.

No forensic technique is foolproof, and nobody should be on a criminal database for life on the basis of a teenage traffic infringement or anything like it. Where DNA is taken voluntarily from people for purposes such as eliminating innocent samples at a crime scene, the samples should be destroyed.

DNA fingerprinting is astonishingly accurate, matching samples to the point of concluding a suspect is several thousand million times more likely than anyone else to be the culprit.

But that is not infallibility. It is a tool that depends on the quality of its database as well as its quantity. Quality is not well served by subterfuge and manipulation. Fair and open sampling serves the best interests of law-enforcement, with the liberties we must preserve.