Justice and DNA
I support the existence, with proper controls, of a DNA database to help convict the perpetrators of serious crimes. However, the debate around the issue is a lot more complicated than some people would have you believe.
Concerns about this issue are not just about protecting the civil rights of criminals. They are about making sure that that DNA is not misused or misunderstood in ways which lead to the wrongful conviction of innocent people.
For a start, if courts and police forces were foolish enough to imagine that you can safely seek a conviction on DNA evidence along - and fortunately most of Britain's police forces are not that stupid - you would have a recipe for wrongful convictions of the innocent based on misunderstandings of the probabilities involved.
Remember Professor Sir Ray Meadow? He was one of the most distinguished paediatricians in the country but his brilliance as a doctor was combined with an ignorance of statistics in general and conditional probability in general was worse than would be expected of a VI former studying maths. His misunderstanding of conditional probability led him to seek to persuade juries that a number of women, at least three of whom were almost certainly innocent, had murdered their own children. His erroneous testimony directly resulted in at least two wrongful convictions and appears to have indirectly caused the death of one of the innocent women wrongly convicted of murdering her own children.
I cite this case to make the point that the lives of innocent people can be wrecked if courts are wrongly advised of the probabilities surrounding any form of science relevant to a crime. And as I wrote in a blog post about Sir Ray a couple of years ago, potential risks of miscarriage of justice if scientific statistics are presented to a court in a misleading way are not a problem unique to cases of cot death. DNA evidence carries the same risk.
While genetic fingerprinting and DNA matching are an immensely powerful tool and there is no doubt whatsoever that it has enabled many guilty people to be convicted, the evidence has to be used and described properly. Statements of probability in relation to genetic evidence can sound more powerful than they really are unless there is corroborative evidence.
Let’s give an example. Supposing there is a crime for which there are no surviving witnesses, and the police have recovered genetic material which they are absolutely confident belongs to the perpetrator. A check of the national DNA database finds one match with a potential suspect and the DNA match is sufficiently good match that only one person in five million would have a fit as good as better. The suspect is tracked down and brought in for questioning, and the police find that he could have been in the right place at the right time and has no convincing alibi.
It is my understanding that most British police forces would do more work than this before bringing a prosecution, but let’s suppose for the sake of argument that we have a rare sloppy example, and they don’t. You are on the jury – you are told that the accused had the opportunity to commit the crime and that genetic fingerprinting suggests it is five million to one that he did it. Do you find him guilty?
If you said yes, I hope you’re not on the jury should I ever be wrongly accused of anything. Five million to one odds means there are about eleven people in Britain with an equivalent match, including about three or four adult males of an age to be strong and fit. We would need far more evidence against the accused than just the statistics before to be confident that we were convicting the right man, so that the court could rule out all other potential suspects with an equally good genetic fit.
And sadly, if you want evidence that people in senior positions do not all understand the statistics around issues of conviction using DNA evidence, you only need to consider the following statement from a recent speech by the Prime Minister ..
“I say to those who questioned the changes in the Criminal Justice and Police Act 2001, which allowed DNA to be retained from all charged suspects even if not found guilty: if we had not made this change, 8,000 suspects who have been matched with crime scenes since 2001 would in all probability have got away, their DNA having been deleted from the database. This includes 114 murders, 55 attempted murders, 116 rapes, 68 other sexual offences, 119 aggravated burglaries, and 127 drugs offences”.
(Gordon Brown, 17th June 2008, in a speech on 'Liberty and Security')
This claim by the Prime Minister was examined by a pressure group called Genewatch UK, and forensically torn to pieces, in a report which is available online at
Genewatch tracked back the sources for the Prime Minister's speech. Those sources make clear that the figures quoted are based on estimates rather than the tracking of actual cases, and those estimates are based on a number of unverifiable assumptions. Genewatch demonstrate conclusively that the way Gordon Brown used the figures ignores the fact that many of the genetic matches referred to did not lead to even a prosecution, never mind a conviction, because many matches with DNA found at crime scenes are with people other than the perpetrator such as victims and passers by, or are false matches.
Genewatch's conclusions, which I don't believe any open minded and intelligent person who has read their report could dispute, are that
1. The Prime Minister’s claim that “in all probability” 114 murderers would have walked away had innocent people’s records not been retained on the National DNA Database is false.
2. Ministers are well aware that this claim is false;
3. This figure is seriously misleading to members of the public who are concerned about the implications of retaining innocent people’s records indefinitely on the National DNA Database.
They also put forward evidence to the opinion, which I find compelling, that improved collection and retention of DNA found at crime scenes will improve rates of conviction of the guilty, but that retaining the DNA of those who have not been convicted of any crime will not. One example of the evidence they quote is the following statement from the Nuffield Council on Bioethics:
“…There is very limited evidence indeed that the retention regime of England and Wales is effective in significantly improving detection rates…The match rates between stored subject profiles and new crime scene profiles loaded onto the NDNAD in England and Wales, which is 52 per cent, can be contrasted with that of the Scottish DNA Database, which has a higher match rate of 68 per cent. This demonstrates clearly that the more limited retention policy in Scotland does not necessarily negatively impact upon its subsequent
The Genewatch report quotes the concerns expressed by the British Academy of Forensic Sciences about the disadvantages of profiling everyone at birth, as some of the more hardline advocates of using genetic data have suggested.
For example, if a complete genetic record of everyone in the country was taken, and was then stolen, it would put everyone in the country at risk of being framed by having our DNA planted at a crime scene.
A year ago I would have dismissed that argument as ridiculous. After the government managed to lose discs containing the addresses, birth dates and bank details of 25 million people, I can no longer do so.
So where do we go from here?
The National DNA Database should continue to be improved and expanded, and is an appropriate tool to use in criminal investigations, with more effort made to improve the collection and retention of DNA from crime scenes. However, this should go hand in hand with safeguards to prevent the accidental or deliberate misuse of DNA data to convict the innocent.
There is a need to strike a balance in respect of the information made available to the police: at the moment I think the balance struck by the Scottish parliament looks more appropriate than that which the 2001 act lays down for England and Wales. To quote Genewatch UK,
"The Scottish Parliament voted against indefinite retention of DNA profiles and samples from persons acquitted or not proceeded against, in May 2006. Instead, police powers were expanded to allow temporary retention (for up to 5 years, with judicial oversight) from a much smaller number of people who had been charged but acquitted of a serious violent or sexual offence. The Scottish Government is currently conducting a review of this decision in order to assess whether the temporary retention of data from this more limited category of unconvicted persons is appropriate. In conducting its review, the Scottish Government has expressly ruled out the indefinite retention of fingerprint and DNA data acquired from individuals who are not convicted of any crime.
The Scottish Parliament reiterated its position in a vote on 28th February 2008, rejecting the blanket retention of DNA samples and fingerprints, and recognising that “appropriate utilisation of DNA samples and fingerprints can play an important role in identifying offenders but that it is vital to strike the right balance between prosecuting criminals and protecting the innocent”.
And another safeguard, as I have long argued, should be the provision of better support to Juries on how to use and understand any statistics which may be quoted at them by prosecution and defence alike.