The NZ government passed a law through this morning that allows the Police to collect DNA and fingerprints from any person that they will charge Parliament passes DNA law. This is different from the current situation where only people who are convicted of a crime that carries a sentence of seven years imprisonment or more have their DNA collected.
As I’ve said previously, personally I have no problem with the NZ Police being given greater powers to collect DNA samples from individuals who will be charged with an offence. At present, DNA and fingerprints are collected from everyone who is arrested in England & Wales, regardless of whether or not they are eventually charged. This is currently the subject of heated debate and the government is today in a position of having to make a decision about when and what samples from people who are essentially innocent of any crime are to be removed from the database: see here. Some would say that perhaps the UK has gone too far.
Compared with the UK, the NZ database is relatively small and even with the additional samples being added as the law will now allow, it will remain relatively small. Concern has recently been raised in the UK about whether or not the DNA database has got so big, interpretation is becoming problematic see here – as at 31 March this year, there were DNA profiles from 4.86 million individuals on the database (http://www.npia.police.uk/en/docs/NDNAD07-09-LR.pdf). Particularly from the first link I note that “there are strong statistical arguments against the application of such a large database in forensics. Not only does the complexity of storing and searching such a large body of data increase substantially with the size of the database, but so too does the probability of errors, duplicates and false entries. Moreover, the chance of getting a false positive match is also much higher, simply due to the vast number of comparisons involved and the percentage of the population who have similar (or identical) DNA fingerprints.”
Cold case reviews in the UK have shown that successful matches can be obtained from people who have previously committed a serious offence and then more recently have had to provide DNA and fingerprints in relation to minor offences such as traffic violations. The beauty of cold case reviews is that DNA can solve crimes that occurred before the use of DNA as a crime fighting tool became widely known. A lot of criminals who committed offences in the 1990s or before probably didn’t even realise that they deposited anything worth collecting at the crime scene. Only the foresight of police and scientists meant that samples were collected and are now available for testing. In NZ, the first case that springs to mind that could have been solved one way or the other if samples had been kept for future analysis is that of David Bain, but samples were not kept and now cannot be analysed.
Overall, I think that if managed correctly and with an eye on what has happened in other countries that have already been along this route, the use of such a DNA database in current and cold cases is potentially of great assistance in solving crimes. It is, however, important that users and interpreters of the database understand and acknowledge any potential failings as the database grows and not blindly accept everything that is suggested by the database. Experience in the UK has told them not to rely solely on DNA hits to successfully prosecute cold cases and I personally am always more comfortable with a multi-disciplinary approach to crime investigation.