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Since its introduction in the mid-1980s, analysis of DNA has taken a central place in many criminal prosecutions. Initially, the technology used to carry out DNA analysis came with some major limitations, such as being of low sensitivity – needing relatively large amounts of DNA (say from a drop of blood) to allow for a meaningful match to a suspect’s profile to be made. From the late 1990s to mid-2010s, the test kit used in the UK (SGM Plus) targeted just 11 areas of the DNA and gave a much higher sensitivity than the original technology, enabling DNA profiles to be obtained from small samples commonly invisible to the naked eye – and sometimes consisting of only a handful of human cells. Further sensitivity was achieved in the late 2000s with introduction of enhancement techniques (such as LCN and DNASense), which enabled analysis of very small or ‘low template’ DNA samples. Any match was usually expressed as a random match probability (RMP) – ie the likelihood of such a match coming from an unknown person, other than and unrelated to the suspect.
As these new techniques started to feature in casework, challenges were made to their admissibility, as well as to that of computer-generated statistical evaluation of mixed profiles with multiple potential contributors. Given the random effects which could arise when very low quantities of DNA material are analysed, and which could render unreliable any results obtained, the appellate courts permitted expert admissibility challenges to be made where the quantity was below the so-called ‘stochastic threshold’ (see eg R v Reed & Reed [2009] EWCA Crim 2698). Challenges were also made to the admissibility of statistics generated by newly developed computer software – which, it was argued, had not been sufficiently validated and whose results were thus potentially unreliable (see eg R v Dlugosz [2013] EWCA Crim 2).
Statistical robustness and sensitivity were improved by the arrival of DNA-17 in 2014, a collection of DNA profiling kits that can identify up to 34 individual DNA components at 17 areas of DNA. Nowadays, the use of DNA-17 and specialist software to analyse complex DNA mixtures has become commonplace, and these techniques and programmes have to pass stringent validation processes – backed up by guidelines issued by the Forensic Science Regulator, a post created in 2008, but only placed on an independent statutory basis in 2021.
As a result, challenges to the admissibility of DNA evidence have now all but disappeared. But while the fact of a match can rarely be questioned, the new battleground is over how and when an individual’s DNA got deposited at a crime scene. Microscopic amounts of DNA can be transferred from one surface to another (and then possibly to yet another) with surprising ease, leading to the very real possibility that an individual identified from a matching DNA profile at a crime scene played no part whatsoever in an alleged crime, and that their DNA got there through innocent secondary (or even tertiary) transfer. Additionally, only rarely can it be said when that transfer took place. For further consideration of this topic, see reviews by van Oorschot et al 2021 and Meakin et al 2021.
The appellate courts have started to recognise these dangers. In R v Tsekiri [2017] EWCA Crim 40 (where a conviction based on a DNA match alone was upheld), one of the factors highlighted by the court in deciding on a case to answer is whether it is more or less likely that the DNA profile in question was deposited by primary or secondary transfer. If secondary deposition is the more likely scenario, then DNA alone may not be enough to sustain a conviction.
© Getty images/iStockphoto
What is on the horizon in the field of forensic DNA analysis? Technology that will enable individual profiles to be generated from mixtures currently too complicated to interpret. Technology that will also raise difficult moral and privacy issues, as more personal areas of DNA are targeted (such as those indicating skin colour or ethnicity), in contrast to the non-coding or ‘junk’ areas that are currently examined.
DNA is comprised of four building blocks, referred to by the first letter of their chemical names: A, T, C, and G. Traditional forensic DNA analysis examines areas of DNA that contain repeating 4-letter DNA motifs and it is the number of these motifs at different areas in a person’s DNA that can differ between individuals. In recent years, advanced DNA technology, already applied to clinical science that can quickly ‘read’ the actual sequence of letters comprising DNA, rather than simply counting the number of repeating motifs, has made the transition to forensic science. By reading the DNA sequence of these areas of repeating motifs, this advanced technology, known as massively parallel sequencing (MPS) or next-generation sequencing (NGS), can detect more differences between individuals. For example, with the traditional technology, two people might be found to have seven repeats at a particular area, such that their DNA cannot be distinguished at that area. However, analysis with MPS would be able to detect any differences in the sequence of DNA letters that make up those seven repeats, thereby distinguishing the DNA between the two people. This added layer of information, along with the capacity to analyse more areas of DNA simultaneously, enables MPS to have a higher discriminatory power than traditional DNA analysis. It is this enhanced discrimination that means MPS has the potential to enable interpretation of more complex mixtures of DNA. In addition, use of MPS allows the detection of variants in genes that code for physical characteristics, such as hair, eye and skin colour. This power has been harnessed to enable the prediction of these characteristics from DNA, along with prediction of the biogeographical ancestry, or ethnicity, of an individual.
While implementation of MPS to improve mixture interpretation is not particularly controversial, the use of MPS to predict physical characteristics and ethnicity raises a number of legal, ethical and privacy concerns (for a discussion of these issues, see Scudder et al 2018). These issues are mainly due to the move in analysis from ‘junk’ DNA to genes, which can reveal personal information about an individual, such as intimate health information. In particular, few jurisdictions have a proper legal and regulatory framework in place for this type of analysis. Legislation was passed in The Netherlands in 2003 allowing genetic prediction of limited physical characteristics (Koops & Schellekens 2008). In 2021, in response to the Law Commission review of the Criminal Investigations (Bodily Samples) Act 1995 in New Zealand, the Minister of Justice agreed that the Act is outdated due in part to advancement in technology and these new DNA analyses impacting on an individual’s privacy and human rights, recommending that the New Zealand government create a new Act. Furthermore, as with any new technology to be used to generate evidence for court, a thorough validation and understanding of its limitations is required at all stages of the process: use in the laboratory, interpretation by appropriately trained experts, and communication to the court in a manner that does not overstate the evidence. That said, use of MPS to predict physical characteristics and ethnicity has been implemented in casework in the US since 2017 (Wienroth 2020), in Australia since 2018 (McNevin 2019), across a range of European countries in recent years (Gross et al 2021), and now Cellmark Forensic Services in the UK has been accredited to offer these services to its law enforcement partners since October 2021.
A quote from the comic book Spiderman, yet appropriate here, when we consider the implications of the aforementioned issues of DNA transfer to use of MPS technology. It is important to understand the limitations of predicting a person’s physical appearance from DNA, not just because it is not an exact science and requires probabilities to be considered, but because the DNA being analysed might not actually come from a person involved in the crime. That DNA could have been there before the crime was committed or innocently transferred there during or after the crime.
As the new technology allows for a greater number of profiles to be identified within complex mixtures, so the number of suspects will increase – leading to an increased possibility of totally innocent persons becoming wrongly implicated in crimes. On the other hand, as long as privacy issues are sensitively handled, that same technology can clearly have an important intelligence, rather than necessarily evidential, role. Being able to identify potential physical characteristics will enable investigators to focus their efforts more accurately. There is, however, also a danger that overreliance on DNA could lead to insufficient effort being put into gathering other, more traditional evidence types, which could connect (or exculpate) a suspect to a crime.
What is clear is that DNA evidence is very much here to stay, and lawyers will need to keep abreast of developments, so that it can be properly scrutinised within the trial process.
David Bentley KC is joint head of crime at Doughty Street Chambers. He has a wide ranging defence practice encompassing both trial and appellate work. He is co-author of the DNA chapter in the latest edition of Rook and Ward on Sexual Offences (Sweet and Maxwell: 6th edn 2021).
Dr Georgina Meakin is a Senior Lecturer in Forensic Science at the University of Technology Sydney and an Honorary Associate Professor at University College London. Georgina’s research focuses on investigating the transfer, persistence, prevalence and recovery of DNA and other trace evidence. She is particularly interested in the indirect transfer of DNA and how this affects the evaluation of trace DNA in casework, and continues to provide advice and consultancy in casework in the UK, USA, Australia and Canada.
Since its introduction in the mid-1980s, analysis of DNA has taken a central place in many criminal prosecutions. Initially, the technology used to carry out DNA analysis came with some major limitations, such as being of low sensitivity – needing relatively large amounts of DNA (say from a drop of blood) to allow for a meaningful match to a suspect’s profile to be made. From the late 1990s to mid-2010s, the test kit used in the UK (SGM Plus) targeted just 11 areas of the DNA and gave a much higher sensitivity than the original technology, enabling DNA profiles to be obtained from small samples commonly invisible to the naked eye – and sometimes consisting of only a handful of human cells. Further sensitivity was achieved in the late 2000s with introduction of enhancement techniques (such as LCN and DNASense), which enabled analysis of very small or ‘low template’ DNA samples. Any match was usually expressed as a random match probability (RMP) – ie the likelihood of such a match coming from an unknown person, other than and unrelated to the suspect.
As these new techniques started to feature in casework, challenges were made to their admissibility, as well as to that of computer-generated statistical evaluation of mixed profiles with multiple potential contributors. Given the random effects which could arise when very low quantities of DNA material are analysed, and which could render unreliable any results obtained, the appellate courts permitted expert admissibility challenges to be made where the quantity was below the so-called ‘stochastic threshold’ (see eg R v Reed & Reed [2009] EWCA Crim 2698). Challenges were also made to the admissibility of statistics generated by newly developed computer software – which, it was argued, had not been sufficiently validated and whose results were thus potentially unreliable (see eg R v Dlugosz [2013] EWCA Crim 2).
Statistical robustness and sensitivity were improved by the arrival of DNA-17 in 2014, a collection of DNA profiling kits that can identify up to 34 individual DNA components at 17 areas of DNA. Nowadays, the use of DNA-17 and specialist software to analyse complex DNA mixtures has become commonplace, and these techniques and programmes have to pass stringent validation processes – backed up by guidelines issued by the Forensic Science Regulator, a post created in 2008, but only placed on an independent statutory basis in 2021.
As a result, challenges to the admissibility of DNA evidence have now all but disappeared. But while the fact of a match can rarely be questioned, the new battleground is over how and when an individual’s DNA got deposited at a crime scene. Microscopic amounts of DNA can be transferred from one surface to another (and then possibly to yet another) with surprising ease, leading to the very real possibility that an individual identified from a matching DNA profile at a crime scene played no part whatsoever in an alleged crime, and that their DNA got there through innocent secondary (or even tertiary) transfer. Additionally, only rarely can it be said when that transfer took place. For further consideration of this topic, see reviews by van Oorschot et al 2021 and Meakin et al 2021.
The appellate courts have started to recognise these dangers. In R v Tsekiri [2017] EWCA Crim 40 (where a conviction based on a DNA match alone was upheld), one of the factors highlighted by the court in deciding on a case to answer is whether it is more or less likely that the DNA profile in question was deposited by primary or secondary transfer. If secondary deposition is the more likely scenario, then DNA alone may not be enough to sustain a conviction.
© Getty images/iStockphoto
What is on the horizon in the field of forensic DNA analysis? Technology that will enable individual profiles to be generated from mixtures currently too complicated to interpret. Technology that will also raise difficult moral and privacy issues, as more personal areas of DNA are targeted (such as those indicating skin colour or ethnicity), in contrast to the non-coding or ‘junk’ areas that are currently examined.
DNA is comprised of four building blocks, referred to by the first letter of their chemical names: A, T, C, and G. Traditional forensic DNA analysis examines areas of DNA that contain repeating 4-letter DNA motifs and it is the number of these motifs at different areas in a person’s DNA that can differ between individuals. In recent years, advanced DNA technology, already applied to clinical science that can quickly ‘read’ the actual sequence of letters comprising DNA, rather than simply counting the number of repeating motifs, has made the transition to forensic science. By reading the DNA sequence of these areas of repeating motifs, this advanced technology, known as massively parallel sequencing (MPS) or next-generation sequencing (NGS), can detect more differences between individuals. For example, with the traditional technology, two people might be found to have seven repeats at a particular area, such that their DNA cannot be distinguished at that area. However, analysis with MPS would be able to detect any differences in the sequence of DNA letters that make up those seven repeats, thereby distinguishing the DNA between the two people. This added layer of information, along with the capacity to analyse more areas of DNA simultaneously, enables MPS to have a higher discriminatory power than traditional DNA analysis. It is this enhanced discrimination that means MPS has the potential to enable interpretation of more complex mixtures of DNA. In addition, use of MPS allows the detection of variants in genes that code for physical characteristics, such as hair, eye and skin colour. This power has been harnessed to enable the prediction of these characteristics from DNA, along with prediction of the biogeographical ancestry, or ethnicity, of an individual.
While implementation of MPS to improve mixture interpretation is not particularly controversial, the use of MPS to predict physical characteristics and ethnicity raises a number of legal, ethical and privacy concerns (for a discussion of these issues, see Scudder et al 2018). These issues are mainly due to the move in analysis from ‘junk’ DNA to genes, which can reveal personal information about an individual, such as intimate health information. In particular, few jurisdictions have a proper legal and regulatory framework in place for this type of analysis. Legislation was passed in The Netherlands in 2003 allowing genetic prediction of limited physical characteristics (Koops & Schellekens 2008). In 2021, in response to the Law Commission review of the Criminal Investigations (Bodily Samples) Act 1995 in New Zealand, the Minister of Justice agreed that the Act is outdated due in part to advancement in technology and these new DNA analyses impacting on an individual’s privacy and human rights, recommending that the New Zealand government create a new Act. Furthermore, as with any new technology to be used to generate evidence for court, a thorough validation and understanding of its limitations is required at all stages of the process: use in the laboratory, interpretation by appropriately trained experts, and communication to the court in a manner that does not overstate the evidence. That said, use of MPS to predict physical characteristics and ethnicity has been implemented in casework in the US since 2017 (Wienroth 2020), in Australia since 2018 (McNevin 2019), across a range of European countries in recent years (Gross et al 2021), and now Cellmark Forensic Services in the UK has been accredited to offer these services to its law enforcement partners since October 2021.
A quote from the comic book Spiderman, yet appropriate here, when we consider the implications of the aforementioned issues of DNA transfer to use of MPS technology. It is important to understand the limitations of predicting a person’s physical appearance from DNA, not just because it is not an exact science and requires probabilities to be considered, but because the DNA being analysed might not actually come from a person involved in the crime. That DNA could have been there before the crime was committed or innocently transferred there during or after the crime.
As the new technology allows for a greater number of profiles to be identified within complex mixtures, so the number of suspects will increase – leading to an increased possibility of totally innocent persons becoming wrongly implicated in crimes. On the other hand, as long as privacy issues are sensitively handled, that same technology can clearly have an important intelligence, rather than necessarily evidential, role. Being able to identify potential physical characteristics will enable investigators to focus their efforts more accurately. There is, however, also a danger that overreliance on DNA could lead to insufficient effort being put into gathering other, more traditional evidence types, which could connect (or exculpate) a suspect to a crime.
What is clear is that DNA evidence is very much here to stay, and lawyers will need to keep abreast of developments, so that it can be properly scrutinised within the trial process.
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