More people are likely to favour the wider use of DNA testing following the incidents in the NSW town of Wee Waa in the past fortnight.
A Wee Waa woman in her 90s was rape on New Year’s Eve. Wee Waa is a small town. Townsfolk were alarmed at the thought of rapist in their midst. The NSW Police apparently saw it as an opportunity to get support for more widespread DNA databasing than other jurisdictions have envisaged. They arrived in force and began screening every man in the town who would volunteer to give a saliva sample. On Tuesday, 10 days after the test began, a Wee Waa man was charged with the rape after he turned himself in on Monday. It is not known whether he was one of the 500 men who gave voluntary samples in the past 10 days. He did, however, give a sample after he turned himself in.
The simplistic message is that mass DNA testing works. However, though the building up of a DNA database has merit, there are dangers. Moreover, the Wee Waa example, is not a good base for an argument in its favour. DNA evidence is particularly effective in rape cases where the victim is not known to the alleged perpetrator. Once the DNA matches, the only defence left available is consent. On the other hand, in other types of crime, there is plenty of room for uncertainty about the collection of DNA at the crime scene. Hair, fingernails, skin and other DNA-rich material might well be found on the crime scene, but there might be many legitimate reasons for it being there. The accused might be an acquaintance of the victim, or in classic detective-book style, could be the butler or the cleaner. Then there is the difficulty of police, informers, or people with a grudge, placing DNA-rich evidence at a crime scene. Or it could be brought to the crime scene accidentally on clothing, blankets or other artifacts. The question of police planting evidence cannot be ruled out given evidence that has come out in the Wood Royal Commission and Independent Commission Against Corruption hearings. In a rape case, on the other hand, these other ways of the appearance of matching DNA material are not possible.
The least difficulty with DNA is the matching. Given two samples of human tissue, matches can be made with a very high degree of probability. If samples are high grade – blood, saliva or semen – the probability becomes virtually conclusive. The bigger the quantity of the tissue and the better its quality the higher probability of the match. But even with low-grade matches the probability is in the order of saying that only one person in 100,000 would have the same match. Coupled with other evidence it becomes fairly conclusive.
But it is one thing to say the DNA of two pieces of tissue match and another to say the human concerned is guilty of a crime. It is important that police, prosecutors and juries do not become so mesmerised by the matching science that questions of how tissue arrived at a crime scene in the first place are ignored.
The danger with the Wee Waa experience is that people will give DNA testing a magical quality it does not deserve. DNA testing has its place. There is justification for developing a database from people convicted and from samples taken from unsolved crimes, for example. The use of DNA to prove innocence also is important. But any widening of the database must be concomitant with the development of independently verified procedures to ensure the integrity of sample taking and for scepticism by police and prosecutors about assuming that mere presence of a matching sample at a crime scene equates to guilt.
It would be dangerous to use what appears to be a successful use of DNA testing in a rape in Wee Waa as a platform for widespread DNA testing for all forms of crime.