The ACT has long urged for the widest among of DNA sampling at meetings of federal and state ministers. There is some merit in this but there are legitimate concerns.
In Britain the DNA database contains the DNA records of more than 400,000 people. It has helped solve a lot of crime and helped exonerate a lot of victims. In the US, DNA testing is being used decades later to bring people to justice and to exonerated convicted people. In one case of poetic justice, a man has been charged with the murder of a DNA researcher Helena Greenwood. Ms Greenwood scratched at her attacker and pieces of skin under her fingernails were kept after her death and later DNA tested. Police allege a match with a prime suspect, 24 years later.
The criminal justice concerns do not centre around the testing itself. Everyone agrees on the science. If you have two samples of bodily matter – one taken from the accused and one from the crime scene — scientists can DNA test each one to obtain an identifying bar code. If the bar codes match there is no rational doubt that the bodily samples come from the same person (unless they are identical twins).
But getting an exact match, does not of itself prove the person did the crime.
Other questions must be satisfied.
Did Sample B come from the crime scene? It could have been planted.
Was there some legitimate reason for a sample of the accused’s bodily matter being at the crime scene? It couldhave been carried there by someone else. The accused could have been at the scene for legitimate reasons, particularly if a relative or acquaintaince on the victim as so many accused are.
Is there a secure trail from the taking of crime scene sample to the testing stage?
Was there a possibility that the bodily part was taken to the crime scene by unrelated methods?
So the DNA matching might prove to rational certainty that this sample matches this accused, but it does not prove the crime. It is important that these other questions are excluded.
It is important also that juries do not get so awestruck with the DNA evidence that the questions are not asked or satisfactorily answered. The capacity for juries to be awestruck by science is nototious. The Chamberlain case was a classic.
The beauty of DNA testing is its speed, cheapness and ease – both of taking samples and of matching them against an existing database. This is entirely different to fingerprinting where getting good samples is difficult. Criminals wear gloves or do not leave beautifully unsmudged prints on surfaces like glass. Also matching even a good sample with the existing database is difficult even with good computer power.
DNA leaves a more certain mark. DNA is the huge molecule in cells that contains the genetic information of life. It is in all forms of life. The fingerprinting technique was developed in 1984 and later improved so that you can now replicate even a tiny amount of DNA from a tiny sample of bodily matter. Every individual has unique patterns of sequences along the DNA. (Only identical twins have identical patterns.) These sequences do not contribute to genetic traits. Enzymes are used to cut and strand the DNA. They are then hit with some radioactive material that latches on to particular sequences and causes an exposure on x-ray film. The result on the film is like a bar code. If the bar codes match the sample matches the accused’s DNA. If they do not then the sample did not come from the accused’s body.
DNA testing can also reveal whether someone is a relative of someone else. Because siblings have half their genes in common, and similarly with parents and children, a similarity in the DNA pattern can reveal that level of relationship.
In Australia recently a crime was cleared up when a suspect’s DNA was put against a crime scene sample. The match was only half right. In fact the accused’s mother did the crime.
DNA testing helps police eliminate suspects early. This is helpful because often police get fixated on one suspect while the trail for the real perpetrator goes cold.
In Britain DNA testing has been very successful In 40 per cent of cases where there is a DNA sample the case gets solved. Often, faced with the DNA result, suspects plead guilty, saving costly and traumatic trials.
Most crime is done by only a very small percentage of the population. It enables linking of crimes even if there is no suspect, and when much later a match is made, suddenly many crimes are solved. But caution is needed to make sure the sampling evidence has been taken properly and securely.
The question is who goes on the database and for how long are samples and DNA codes kept — everyone, just suspects, just those convicted? There is an argument that because of the potential to clear up so much crime and the potential to exonerate the innocent, samples should be taken from as wide a circle as possible.
The illustration shows the DNA fingerprint from blood (or hair) at the crime scene in the middle and the DNA fingerprint of seven suspects. Suspect No 3 has a perfect match.