DNA and individual freedom v crime prevention

Will the government's Protection of Freedoms Act lead to an increase in murders, rapes and other serious crimes? New research from the United States suggests it might.

The legislation, which became law last May, is resulting in many thousands of DNA profiles being removed from the UK's giant DNA database - people arrested but not convicted of a serious offence after three years. Ministers argue that the previous approach, in which DNA samples were kept indefinitely, undermined the freedom of innocent citizens.

Britain pioneered the use of DNA as a crime-fighting tool, introducing the world's first national database in 1985. Today it holds the profiles of more than five million people and is credited with helping solve some 40,000 crimes a year.

The US, Canada, Australia and most European countries have followed the UK's lead, with DNA profiling internationally regarded as the most important breakthrough in modern policing. Until now, though, there has been little scientific research on whether such databases really do reduce offending.

Last month Jennifer Doleac, assistant professor of public policy and economics at the University of Virginia, published a paper entitled The Effects of DNA Databases on Crime, which suggested that size matters: "larger DNA databases reduce crime rates".

The paper estimates that each new profile added to the US DNA database - the Combined DNA Index System, or Codis - resulted in 0.57 fewer serious offences. Uploading a profile costs about $40, which means that in 2010 the database cost the American taxpayer $30.5m but, according to the research paper, saved a whopping $21bn in crime prevention.

Retaining DNA from individuals who are not convicted of an offence is as controversial in the US as it is in the UK. Some American states do keep samples from people arrested but not convicted while others do not. So the University of Virginia study was able to compare the two approaches.

Ms Doleac calculates that if every state kept the profiles of people arrested but not convicted, the US would see a fall of 3.2% in murders, 6.6% in rapes and 5.4% in vehicle thefts.

DNA advances have also resolved miscarriages of justice such as the case of Sean Hodgson

This conclusion flies in the face of current British government policy that does the opposite. In a Commons debate in October 2011, Home Office Minister James Brokenshire challenged the suggestion "that the more people's DNA is on the database, the more effective it is".

He made the point that in 2004/5 there were 2.8 million people on the database and 35,605 detections. In 2009/10 there were 4.8 million profiles but 32,552 detections.

However, it's also true that in 2008/9 there were 79 murder, manslaughter or rape cases in which DNA was matched to individuals who had been arrested but not convicted.

The Labour party argues that profiles of people arrested but not convicted should be kept for six years rather than three. The Association of Police Officers says even that change would lead to an extra 1,000 crime/profile matches a year.

With the murder rate in England and Wales now at its lowest level since Jim Callaghan was prime minister, there are many theories as to why violent crime has seen such a significant fall in recent years. One answer is the DNA database.

It is broadly accepted that there is a balance to be struck between crime prevention and individual freedom. This new research adds a little more evidence to help decide where the balance should lie.