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DNA: A Cautionary Tale

October 01 2011

Forensic Science Interpreting The Evidence

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DNA Profiling

Evidential evaluation of DNA profiling evidence received significant guidance from the Court of Appeal in R v Alan Grant [2008] EWCA Crim 1890.

Unlike other judgements guiding experts on how to interpret their findings, this covered the value of an uncorroborated DNA link in specific case circumstances; the DNA profiles not being in dispute.  In essence it was accepted that the major DNA profile from a balaclava was sufficient to link the defendant to it, but not to the act of discarding it near the scene of a robbery.  This highlights the distinction between a DNA profile match providing Police with sufficient evidence to justify a charge and the more rigorous test of being sure. In our experience this is a common dilemma particularly in less high profile or less high profile cases such as burglary, where investigation appears to cease if a DNA profile from some item, believed associated with the offence, identifies a suspect.  Clearly there must be some circumstances, e.g. a blood spot within a burgled house, where a DNA profile match provides compelling prosecution evidence due to lack of a credible alternative.  There are also many that reach Court which fall within the category of R v Grant, where the significant DNA profile was from a mobile or portable object such as gloves, balaclava, clothing, weapon or vehicle; but in itself should not be interpreted as sufficient to link, to the necessary high standard of proof, that person to the offence.

Testing of the balaclava in R v Grant revealed the presence of a minor incomplete DNA profile from at least one other person.  This should however, be irrelevant, as failure to detect any other DNA sources would not have determined whether there had been contact with other people or altered evaluation of the major DNA profile.  Detection of other DNA source(s) on this balaclava would support the suggestion that someone else may have worn it but, because DNA transfer is uncertain, if the testing failed to detect other sources this would not have indicated that Mr Grant was the only wearer.  Irrespective of the degree to which Police forensic budgets are under pressure, we encounter cases where uncorroborated DNA profile matches provide sufficient evidence to identify a suspect and justify a charge, but where those charges remain disputed there is no further forensic effort.  The only apparent explanations seem to be lack of understanding by those responsible for setting the prosecution forensic strategy, unwillingness to seek expert advice or perhaps an over acceptance by the defence of the bald assertions made in prosecution forensic reports.

Keith Borer Consultants have prepared reports in many cases where this has been the main issue.  Forensic findings of this type are individual to each case and consequently very similar DNA profiling results may be compelling in some case circumstances and evidentially worthless in the next.  These cases show the importance of examining with care reports on DNA evidence and on keeping abreast of recent case law developments.

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