Forensic DNAprofiling analysis

In the UK DNA evidence has been presented in courts since the late 1980s and it is now used extensively both in the detection and prosecution of crime.  Since 1988 the techniques involved in DNA profiling have been continuously developing with increasing sensitivity and ability to unambiguously identify an individual.

Since 24th July 2014 the older technique of SGM Plus was superseded in the UK by DNA 17. This latest technology has increased the ability of forensic providers to detect trace amounts of DNA and this enhanced sensitivity of the tests greatly affects the interpretation of the DNA results obtained.  Detailed consideration must be given as to when and how the DNA could have been deposited including any potential contamination or innocent transfer mechanisms. SLS Forensics’ consultants have extensive knowledge and experience of all DNA profiling techniques employed since 1988, including STR (SGM, SGM+, DNA 17) profiling, specialist DNA techniques (including LCN, DNA SenCE, YSTRs and mitochondrial DNA) and historic techniques (such as DQα, MLP and SLP). SLS Forensics can commission re-testing of samples or profiling of stains that have not been analysed by the Crown and we can assess whether the Crown’s analysis could have been contaminated in any way. We can assess the possibility of error given the published error rates for the National DNA Database:

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In addition to any transference issues surrounding the DNA evidence, interpretation can often be made even more complicated if more than one individual has contributed to the result or if the result could originate from more than one type of cellular material. Often when interpreting mixtures of DNA from more than one person the statistical evaluation is not straightforward. Recently computer software such as STRmix™ LikeLTD and LiRa have been used to assist in the statistical evaluation of complex mixed DNA results. SLS Forensics has experience of cases that have utilized these novel techniques and can advise where necessary and carry out independent DNA calculations, using LikeLTD, where appropriate.

Many prosecution statements infer that an individual could be a potential contributor to a complex mixed DNA result but that the result is so complex that no statistical evaluation can be completed. The Appeal Court ruling of R – v – Dlugosz, R – v – Pickering and R – v – MDS, EWCA Crim 2 [2013] represents the current state of the law with respect to DNA mixtures with no statistical evaluation. However, in July 2018 the Forensic Science Regulator issued guidelines that the practice of giving a subjective opinion with regard to the significance of a person being a possible contributor to a complex DNA mixture should be discontinued:

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SLS Forensics’ scientists have had extensive experience of presenting evidence in voir dire. Under appropriate case circumstances this has often resulted in the complex DNA mixture evidence being ruled inadmissible, for example, T20177172 R – v – Richard Day at Northampton Crown Court, July 2018. We are happy to guide Counsel through the complex issues that such DNA evidence presents and any potential admissibility challenges.