Abstract
Although forensic DNA testing is well established, some experts disagree with the interpretation and statistical significance of test results obtained from very small samples. This article discusses the problems regarding the use of the low copy number (LCN) technique as well as the value that can be derived from such an analysis. It focuses on the problematic results that can arise from using very small samples for forensic DNA identification. Since this kind of analysis is based on low amounts of DNA samples (between 100 picograms and 200 picograms in South Africa) that are amplified by using more than the normal 28 cycles to create larger samples for analysis, the reliability of the analysis has been questioned. The amplification process, known as the Polymerase Chain Reaction (PCR), is associated with risks such as stochastic effects and contamination that could make interpretation of the results difficult for the defence. While standard operating laboratory protocols could prevent contamination and although the electropherograms could aid the detection of contamination, it is highly problematic for the defence counsel to ascertain whether these procedures were indeed strictly followed. Drawing on foreign jurisprudence, this article considers the risks and key controversies and explains what lawyers need to know, in order to be able to recognise controversial results that could stem from using the LCN DNA technique for forensic DNA identification. The conclusions thus drawn may be of particular relevance to the South African context, as no reported case law exists in which the issues relating to the use of LCN DNA have yet come to the fore.
Highlights
Gill adapted Van Oorschot’s definition of trace DNA and describes this phenomenon as “any sample where there is uncertainty that it may be associated with the crime event itself – so that it is possible that the transfer may have occurred before the crime event or after the crime event.”13 The terms “low template (LT DNA)”, “low copy (LCN)” or “trace/touch DNA” refer to deposited DNA that weighs less than 200 picograms
Only samples that are above 100 picograms and below 200 picograms are tested in South Africa by the low copy number (LCN) method, the problems that pertain to Low copy number DNA (LCN DNA) testing are applicable to the South African situation
Weir J pointed out in the Hoey case that “justice ‘according to law’ demands proper evidence ... evidence which is so convincing in truth and manifestly reliable that it reaches the standard of proof beyond reasonable doubt”,129 but the evidence, which was primarily based on LCN DNA evidence, was found to fail the required standard of proof
Summary
Forensic DNA testing is well established, some experts disagree with the interpretation and statistical significance of test results obtained from very small samples. It focuses on the problematic results that can arise from using very small samples for forensic DNA identification. Since this kind of analysis is based on low amounts of DNA samples (between 100 picograms and 200 picograms in South Africa) that are amplified by using more than the normal 28 cycles to create larger samples for analysis, the reliability of the analysis has been questioned. Drawing on foreign jurisprudence, this article considers the risks and key controversies and explains what lawyers need to know, in order to be able to recognise controversial results that could stem from using the LCN DNA technique for forensic DNA identification. The conclusions drawn may be of particular relevance to the South African context, as no reported case law exists in which the issues relating to the use of LCN DNA have yet come to the fore
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