DNA Evidence | Current Issues

DNA Evidence | Current issues

In response to an invitation I addressed the latest meeting of the New Zealand Law Society (Wellington Branch) held at the Law Society building in Wellington, New Zealand, on the 18^th of June 2015.  My brief was to try and shed greater light on DNA evidence, an evidence type that members often find confusing. The confusion, I suggest, arises from the terminology and vocabulary used which, in many cases, offers little clue as to meaning. DNA evidence is in fact a combination of chemistry, biology (and a number of sub- branches) and statistics. The same term can have different meanings depending on the science, e.g. to a chemist ‘sensitivity’ is the gradient of a response curve (the size of the signal for a given change in parameter measured) and to a biologist the limit of detection/quantitation (how little can be detected). If scientists can be confused what hope for lawyers?

 

SWGDAM offers a helpful glossary but even then confusions remain, e.g. what is and what is not a random or stochastic effect?

 

Interpretation of complex mixtures (more than two contributors)

After an introduction to the chemistry, biology and statistics behind the evidence type the discussion broadened to current issues.   These issues stem from the ability of the latest profiling products to obtain a DNA profile from just a few cells. The results are very often mixed or complex profiles where there is evidence of more than two contributors. How to interpret these complex profiles has been the subject of much debate over recent years and I think it is fair to say that consensus has yet to emerge.

 

Different labs use different approaches, making different assumptions which obviously yield different results. It could be argued that until consensus is reached the interpretation of complex mixtures should be restricted to use as an investigative tool rather than be adduced as evidence. If science is undecided then what help can it be to the trier-of-fact? 

 

Secondary transfer and Contamination

Other consequences of technological advances are that contamination and secondary transfer become more problematic. One of the fundamentals that assure the forensic utility of DNA evidence is the fact that human beings shed cellular material. Given the large numbers of cells shed, an individual’s cells will transfer by whatever means are available. The finding of an individual’s cellular material at a crime scene may not be evidence of presence. Innocent individuals might find themselves the subject of police enquiries, a situation that should be of concern to citizens and legislators.

 

Anti-contamination procedures become increasingly complex, burdensome and expensive. As complexity increases so does the risk of failure and error.

  

Interpretation and software packages STRmix^TM

The discussion then turned to more parochial matters. The New Zealand forensic science provider ESR is using ,and commercially marketing, a complex mixture interpreter: STRmix^TM. Given that ESR, with its Australian partner, are looking to sell this software package overseas it seems likely that intellectual property issues may be used as an excuse to close the product off from independent scrutiny (so called ‘black boxing’). However, the recent admission by the FBI of errors in its DNA evidence going back to 1999 provides compelling support for the argument that the validation data and all relevant studies for DNA interpretation software must be open to independent scrutiny.

 

Laboratory Error

A step in the interpretation of DNA evidence is the calculation or estimation of a random match probability – the chance of a false positive. Given a full profile and one major contributor this is often an unimaginably large figure. Advances in technology, specifically the addition of extra loci (CODIS 20  and DNA 17), have the potential to significantly increase this number such that the likelihood of laboratory error may have to be taken into account when interpreting DNA evidence.

 

Investigative v Evidential value

Perversely, technological advances have the potential to reduce the probative value of DNA evidence.  Advances certainly improve its utility as an investigative tool but the complexity of the interpretation can put the evidence beyond the understanding of the average juror.

 

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ISO 17025 is not a 'gold' standard

On the 17^th of June 2015 the BBC website reported that, as a result of the fall in the number of forensic fibre experts, the killers of Stephen Lawrence might escape justice if the cold case review that led to their conviction was conducted today rather than in 2007.

In that report the international standard ISO17025 is referred to as a ‘gold’ standard. It is not. It is a minimum standard.  

One of the strengths of quality management systems, of which ISO17025 is a part, is that there are only two conditions; compliance or non-compliance. Either a product or service is fit-for-purpose or it is not. If not then remedial action is required to limit the effects of any non-compliant product or service and ensure a speedy return to compliance.

 In my experience, gained in numerous jurisdictions and over the last 25 years, the accrediting body in the UK (UKAS) operates to a high standard. This results in the forensic science laboratories it accredits working to a higher standard than those accredited by other, less experienced, bodies such as ASCLD/LAB and NATA. Nevertheless, even in England and Wales, accreditation to ISO17025 must still be considered a minimum standard.

Compliance with this minimum standard however is significantly better, in terms of delivering justice, than compliance with no standard.

 

Non-accredited forensic science laboratories are used by the police

The BBC reports that the Met (Metropolitan Police) routinely uses non-accredited laboratories.

It seems extraordinary to me that any police force or law enforcement agency would use a non-accredited laboratory. The first forensic science laboratories were accredited in the late nineties, over 15 years ago. Why are there any non-accredited forensic science laboratories providing services to police forces?

It would also be extraordinary if courts did not question the reliability of and closely scrutinise any scientific evidence provided by a non-accredited laboratory.

 

Response by the Forensic Science Regulator

The reassurance of the Forensic Science Regulator, Dr Gillian Tulley, that “The vast majority of forensic work is done to a very high quality” is worthless. Only an accrediting body, such as UKAS, has the competence to determine whether or not a forensic science laboratory and the evidence it provides is fit-for-purpose.