Has DNA become a victim of its own success?

Written 1st June 2016 by Olliers Solicitors

In 1988 Colin Pitchfork was convicted of the rape and murder of two 15 year old girls. As horrific as his offences were the remarkable aspect of his case was that he was the first person to be convicted as a result of DNA evidence. His DNA matched samples found at the scene of both crimes.

In the world of criminal investigation this was a game changer. Between March 2001 and March 2014 the Home Office who run the DNA database has produced nearly half a million matches between suspects and crimes. Just think half a million crimes that would have gone unsolved.

At its peak the Home Office held the profiles of 5.7 million people on its database although 1.7 million profiles have been deleted in recent years, following the ruling of the European Court of Human Rights in S and Marper v United Kingdom.

What is DNA?

More remarkable however are the recent developments in DNA. The science is a wonderful and complex thing and there are few people who understand it fully. In simple terms DNA is made up of chemical substances that are linked together like a chain. Each piece of DNA has two long strands and a number of chemicals called bases. The bases connect the two strands and to put the complexity into context each human has about 3 billion strands. Mind boggling stuff.

What is DNA 17?

As science develops, the ability to detect cells has become more and more sensitive. DNA 17 is the latest technique. It looks at 17 areas of a person’s profile. The previous technique ‘only’ examined 11 and when Mr Pitchford was convicted it was four.  It is able to pick up profiles from smaller, poorer and older cells. This of course is to be admired but it can also can pick up fragments of DNA unconnected to a crime. An extreme example, although possible, is a passer–by who inadvertently transferred their DNA to a victim of crime at a bus stop or some other innocuous place. In Mr Pitchford’s day this would not have been detectable.

Is DNA 17 too sensitive?

Forensic scientists complain that DNA 17 is a victim of its own sensitivity. Scientists are being asked to consider the results of DNA 17 testing from such a small number of cells so that no conclusion can be reached that would stand upto the criminal standard of scrutiny. There is also the added risk that contamination at the scene of a crime is more of a problem, because of the increase risk of detection.

Although the advantages of DNA 17 are obvious, it also runs the risk of over complicating a science and method of investigation with potentially negative consequences or at the very least give an accused a chance to muddy already cloudy waters.

Max Saffman – Specialist Criminal Defence Lawyer

Written by Max Saffman. Max is a specialist Higher Court Advocate and has extensive experience across the full spectrum of criminal offences.


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