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Junk science or junk evidence?

June 01 2015

Forensic Science Interpreting The Evidence

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DNA Profiling

The recent article by Alastair Logan OBE (LINK) accurately describes the current crisis in forensic science provision, except for the title – “Junk science threat to justice”.  The commercial forensic laboratories are generally producing reliable test results, which police interviewers and prosecution case managers/advocates then seem to turn into dangerously inaccurate evidence with pseudo-scientific interpretations and unsustainable inferences.  The science itself is now better than it has ever been.  The accuracy with which it is applied to the criminal justice system has degenerated and continues to get worse.  Junk scientific evidence is the problem.

The examples are numerous, including:

  • Suspects being pressured to account for why ‘their DNA’ was on an item, when they are no more than one possible contributor to a complex mixed profile
  • Suspects being told that the DNA evidence means they must have had recent contact with an item when indirect secondary transfer, with no direct contact, is equally possible.  This is a common unsustainable prosecution assertion in cases where DNA profiles are the only evidence in allegations of possession of firearms or drugs.
  • Prosecution suggestions that fingerprints or DNA deposits could only have been present at a scene for a short time, when they could have been there months, even in cases where fingerprints or DNA from other people with legitimate access, which must have been there for longer, were detected. Research directly contradicts this common prosecution assertion.
  • Prosecution forensic experts being asked to evaluate the results on the basis that ‘the defendant could not account for his DNA on an item’, when they had attempted to provide an explanation or where simple re-distribution of DNA in a domestic or social environment could account for the results.
  • A single blue wool fibre presented as strong evidence to associate a man with a sex attack, without any knowledge of the previous context or what the two people might have been doing in the same area prior to the offence.
  • Widespread failure by police/prosecutors to apply appropriate forensic strategies to cases, compounded by then predicting the results to be valueless when the defence wish to commission potentially probative forensic tests.

There can be no doubt that sound scientific test results are frequently converted into misleading and inaccurate evidence, with the inherent danger of miscarriages.  Those with responsibility for policy seem immune to the obvious consequence, that this all means a greater error rate for the criminal justice system.

Dr Duncan Woods, Chief Scientist

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