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Disputed DNA Fingerprinting Trial Evidence: How Sure Is It Possible To Be?

written by: Ollie Hicks•edited by: Paul Arnold•updated: 6/27/2011

The development of DNA fingerprinting and its use in the courts has helped us all feel a lot more secure about the justice of criminal trials. But can problems arise with DNA evidence? Are all the techniques involved as reliable as we might like them to be?

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    Just How Reliable Is DNA Fingerprinting?

    The advancement and enshrining of DNA fingerprinting as an investigative and prosecutorial tool is a great psychological comfort. The apparent certainty it provides in targeting the wrongdoer and keeping the innocent safe from wrongful prosecution is a bulwark against fears of the slings and arrows of fate and indeed active malice. But does it really provide the security and cast-iron certainties it seems to offer?

    Reliance on DNA fingerprinting has become commonplace in UK criminal trials since the 1980s.1 However in recent years there have been questions regarding whether it is the magic formula we may feel we were promised, inoculating the justice system against wrongful convictions.

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    Are All DNA Profiling Techniques Equally Accurate?

    Reportage of the Omagh bomb trial (regarding the terrorist attack in Northern Ireland in which twenty-nine people died in 1998) is relevant. Expert witnesses questioned the reliability of the low copy number DNA evidence used. (Low copy number procedures - LCN - allow DNA profiling from extremely minute samples). Some press coverage at the time seems to hint at the possibility of DNA contamination due to procedures in place regarding laundry of lab clothing.2

    Not all types of DNA evidence are created equal, it seems: advances have been made in the quantity of a sample required and the match probability that can be achieved, but a trade-off may be required between the two.1 The question of how well juries can understand the DNA evidence presented to them has also been raised.3

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    DNA Fingerprinting History and The Wrongfully Convicted

    Through famous endeavours such as, we have become used to stories about innocent people wrongfully convicted and being freed due to the wonders of genetic fingerprinting.4 For example Kirk Bloodsworth, who was the first person to be sentenced to death row to be exonerated by DNA evidence, an important case study for students of DNA fingerprinting history.

    An article by Paul Johnson and Robin Williams (based on a DNA exoneration case in the UK) points out that new DNA evidence provided post-conviction may not be enough on its own to give a cast-iron proof of innocence. They contend that its real value is when it is combined with other forms of evidence such as eyewitness accounts and expert testimony. Johnson and Williams caution against the level of importance attributed solely to DNA fingerprinting, viewing it instead as a valuable piece of a larger puzzle.

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    Application Of Improvements In DNA Forensics

    In the end, if more stringent criteria for scientific evidence (and therefore the application of scientific advances) are applied to criminal cases, then surely this can only improve the success and fairness of a criminal justice system. As knowledge and techniques improve, it is reasonable to expect this to apply to different techniques of DNA fingerprinting also and to their application in law.

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    1. The Crown Prosecution Service. 'Chronology of Developments in DNA Profiling.' 1999 (29/08/2009). <>

    2. BBC News. 'Omagh DNA evidence 'unreliable.' 16/11/2006 (29/08/2009) <>

    3. Findlay, M. 'Juror comprehension and the hard case—Making forensic evidence simpler .' 2007 (29/08/2009) <>

    4. Innocence Project. 'About The Innocence Project.' 30/08/2009 (29/08/2009) <>

    5. Johnson, P. and Robin Williams. 'Post-conviction DNA testing: the UK's first ‘exoneration’ case?.' 25/01/2006 (29/08/2009). <>

    6. Berger MA. The Technology of Justice: DNA and the Criminal Justice System. John F Kennedy School of Government; Harvard University: 2001. Lessons From DNA: Restriking the Balance Between Finality and Justice.