Voices of Forensic Science

Chapter 3 The Contamination and Misuse of DNA Evidence Vanessa Toncic, Alexandra Silva "Genes are like the story, and DNA is the language that the story is written in." (Kean, 2012) To understand how potentially mishandled or contaminated DNA evidence could be manipulated or presented in court, (under false pretenses), as an evidentiary ‘gold standard,’ it is important to first explain why, and under what circumstances, DNA evidence is in fact a gold standard. DNA evidence may be disguised as a gold standard when either the techniques used, or the representation of the data has been skewed and is no longer reflective of DNA as a gold standard. This chapter will explore the use of mixed DNA profiles as well as low copy number (LCN) techniques of DNA analysis, and how these methods may not be deserving of the ‘gold standard’ seal associated with DNA evidence. We will explore the biological aspect of issues with these methods and how they may reflect a contaminated DNA sample. Notably, DNA evidence that has been appropriately collected and analyzed may still be purposely misrepresented to a judge and/or jury. DNA as an evidentiary gold standard requires proper handling from the onset of collection, throughout analysis and storage, as well as during presentation in court to ensure that the quality of evidence is upheld. DNA evidence and its associated challenges are multi-faceted areas of study. These studies include issues surrounding the collection as well as the analysis of evidence leading to subsequent contamination and root cause analysis. There also exists debate on the ethics and privatization of DNA given the popularization of online DNA databases. The longstanding use of DNA evidence has also led to the propensity for DNA to potentially overshadow other scientific evidence in a forensic context, and for it to hold considerable weight in a judicial 47 Are We There Yet? The Golden Standards of Forensic Science context. The following chapters will explore these topics and will also consider the future of DNA analysis. DNA as an Evidentiary Gold Standard The impact of DNA should not be understated. DNA analysis is a scientific advancement that can potentially demonstrate factual aspects of an event when used correctly. It is for this same reason that this type of evidence must be used appropriately, as there is great potential to abuse and misuse DNA evidence. DNA was regarded as the ‘gold standard’ of forensic evidence following the 2009 National Academy of Science (NAS) report. It was in this report that it was stated, “[w]ith the exception of nuclear DNA analysis…no forensic method has been rigorously shown to have the capacity to consistently, and with a high degree of certainty, demonstrate a connection between evidence and a specific individual or source” (NAS, 2009, p. 7). This made clear to the international forensic science community that no other evidence type had the capability of being as definitively individualizing as DNA evidence. Gold Plated Issues arise when methods of DNA analysis that are known to be less widely accepted are employed and subsequently presented as an infallible fact of science. In these cases, the DNA evidence is simply gold plated. What appears to be a perfect exterior of unflawed evidence can easily be distinguished as less than satisfactory under further inspection. Specific areas of DNA analysis such as mixed DNA samples and low copy number analysis are methods in which there exists room for error, moreso than in other techniques (Buckleton, 2009; Gill et al., 2006). These techniques are subject to increased bias on behalf of those who analyze and interpret such evidence. DNA samples that are contaminated by multiple DNA profiles or other biological and/or non-biological sources are not reflective of the same level of ‘purity’ as the gold standard of DNA evidence that we have come to know. 48 The Contamination and Misuse of DNA Evidence DNA Mixtures DNA mixtures, or mixed DNA profiles, are samples in which the DNA of two or more contributors are present (Hu et al., 2014). DNA mixture analysis presents a challenge to scientists as the ability to discern individual profiles become more challenging as the number of contributors increases (Hu et al., 2014). A more basic type of mixture contains a known source of DNA from a victim, and an unknown source from a suspect (Hu et al., 2014). The issues of reliability and accuracy in terms of identification of a suspect within a DNA mixture are primarily due to allele drop-in, allele drop-out, and stutter peaks (Hu et al., 2014). Gill and colleagues define allele drop-in as “contamination from a source unassociated with the crime stain manifested as one or two alleles,” where an allele describes the specific variation or trait encoded by a gene (2006, p. 101). In contrast, allele drop-out is a “low level of DNA insufficiently amplified to give a detectable signal” (Gill et al., 2006, p. 101). The difficulty of determining the number and identity of major or minor contributors in a DNA mixture is due to the possibility that the aforementioned factors can both mask allelic contributions as well as over-amplify alleles at various loci, or positions of a gene on a chromosome, in a random manner (Gill et al., 2006). This leads to distortion of the appeared number of contributors at each locus and makes it increasingly difficult to identify the various genotypes at said loci (Gill et al., 2006). Like with any physical evidence, mishandling and contamination are possibilities. In the case of DNA mixtures where multiple DNA profiles are already present in the sample, it is challenging to distinguish allelic drop-in from an additional DNA contributor. The addition of DNA in a sample after it is collected may occur at various instances including during collection or laboratory contamination. It is crucial to distinguish allelic drop-in from a DNA contributor in order for accurate crime-related identifications to be made (Hu et al., 2014). Similar to allelic drop-in, stutter peaks are a potential cause of misidentification in a DNA mixture (Gill et al., 2006). In the case of a DNA mixture that contains both major and minor contributors, a stutter peak of a major allele may be misidentified as a minor allele (Gill et al., 2006). A stutter peak occurs due to slippage of an enzyme during the process of amplifying DNA. It is often considered to be background noise (Gill et al., 2006). 49 Are We There Yet? The Golden Standards of Forensic Science Biedermann and colleagues suggest that “the true number of contributors to a given sample cannot – in view of the currently used STR polymorphisms – be known with certainty” (2012, p. 689). In light of the many criticisms of DNA mixture analysis, the blanket statement that DNA is the gold standard of forensic evidence must be more critically viewed. DNA mixtures allow for greater bias and contamination as compared to a ‘pure’ DNA sample from a single contributor. This is something that a layperson, such as a jury member, is not likely to be aware of. This could impact one’s consideration of the evidentiary value of such evidence. Low Copy Number Profiling By definition, a low copy number (LCN) sample is that which has fewer than two hundred picograms of DNA present, and subsequently fails to meet the stochastic threshold (Budowle et al., 2009). The stochastic threshold allows scientists to be confident that the peak that they are interpreting is reliable enough to be used in their DNA analysis (Budowle et al., 2009). A low copy number sample is inherently ambiguous in nature and more prone to stochastic behavior, meaning it is also not reproducible (Budowle et al., 2009). Reproducibility is a condition one would think is necessary to be classified as a gold standard. When working with LCN samples, increased sensitivity testing may be required to compensate for the reduced concentration of DNA present in the sample (Buckleton, 2009). The caveat to increased sensitivity testing is the possibility of gross contamination or allelic drop-in as previously mentioned (see DNA Mixtures) (Buckleton, 2009). Contamination of a sample that occurs after collection or as the result of a sample mix-up is problematic and is another instance where DNA fails as a gold standard. Gross contamination occurs when a substantial DNA profile is extracted from the sample being analyzed due to contamination (Buckleton, 2009). It is possible that the sample could be contaminated with a suspect’s DNA profile. This could result in a miscarriage of justice as the individual may have had no involvement in the crime, yet the evidence would suggest otherwise. This contamination may also occur from a member of the police, a forensic professional involved in the case, or another individual unrelated to the crime. Increased sensitivity of DNA analysis is greatly susceptible to pre-submission contamination (i.e., the matter in which a sample was handled prior to being submitted to a forensic laboratory) (Buckleton, 2009). The lack of reproducibility of LCN samples in addition to the increased possibility of contamination of the sample must be 50 The Contamination and Misuse of DNA Evidence considered when DNA evidence is broadly labelled as a gold standard of forensic science. Without sufficient training in the natural sciences, it can be difficult to fully comprehend methods used in various forensic science subdisciplines. This may result in the inability to assess the reliability of DNA evidence that is offered in trial. This is a necessary step on behalf of the judge and/or jury in order to ensure a fair trial. Issues may also arise if a forensic professional is not abundantly clear regarding the difficulties associated with analyzing and interpreting DNA mixtures and LCN samples when testifying in court or compiling a report.

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