Advances in forensic science have allowed for a greater reliance on minute quantities of DNA evidence.   Every person’s genetic make-up is unique. This can be beneficial in exonerating the innocent as well as identifying the guilty.

But there is a difference between the full genetic profile of a person and interpreting the forensic evidence in a crime scene on which a match is based.

Evidence based profiles may be incomplete, or a mixture from two or more people. 

Apparently incriminating traces of DNA from bodily fluids or skin cells may have an innocent accidental source or be misidentified based on expectation, particularly in domestic settings where profiles may partially coincide and innocent transfer of genetic material from one person to another is commonplace.

Research has demonstrated that in complex cases, experts’ opinions on DNA interpretation can vary to an alarming degree.  Much may depend on what the expert has been told to look for, so that there is an unwitting tendency towards ‘confirmatory bias’ – where expectation screens out alternate possibilities.

A similar bias has been demonstrated in the interpretation of fingerprints – thought for many years to be 100 per cent accurate.  As with DNA fingerprint profiles may be partial and mixed or caused by innocent transfer.

The trend for ‘evidence-based’ practice has created the popular perception of certainty in forensic science.   But the evidence doesn’t solve itself.  It is fallible human beings who interpret the findings and speak in court and not the evidence.

Juries, lawyers and even judges may be all too easily mesmerized by the way in which spurious but apparently convincing evidence is interpreted and presented – to the detriment of an innocent defendant.

Such cases need careful consideration, independent analysis and legal representatives on top of the subject matter.

In a recent leading case Chris Saltrese Solicitors were commended by the Court of Appeal in overturning a DNA based conviction.  See R v JE  and the article in Inside Time.

Chris Saltrese Solicitors have developed a specialist practice defending and appealing DNA and fingerprint cases.