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Ask Penny

Please post your questions for this week in the comments section below. Penny will select the most liked/interesting questions and publish her response to these on this step by Wednesday of Week 4.

Thank you very much for all of your great comments and questions this week, it’s fantastic to see that you are all still enjoying our case, and that you’re thinking so carefully about the details. You put forward some really great questions about the DNA material, it’s great to see that you’re understanding this topic so well. I hope you find the answers to some of your questions below useful, and remember there will be another ‘Ask Penny’ next week. For those of you who commented that you couldn’t find the answers to the ‘Ask Penny’ questions in Week 1, these were posted on the ‘Ask Penny’ article in Step 1.19.

Anne Martin asked an excellent question about miscarriages of justice, misuse and mismatching of DNA results. There are sadly, some people who have been wrongly convicted as a result of unreliable DNA evidence but there are also those who have been exonerated as a result of DNA testing carried out on evidence that could not be tested at the time. Kim Waghorn also asks about cold case reviews and whilst there is no process to routinely review every case when new DNA techniques are implemented, there are many examples of old cases that have been reviewed and solved as a result of new DNA testing being carried out on old samples that were not tested during the initial investigation of a crime, either because it occurred prior to the widespread use of DNA testing, or because techniques were not sensitive enough at the time to generate a DNA profile from a small amount of sample. Often, the individual who committed a crime is caught many years later as a result of a chance encounter with the police that results in a DNA profile being taken and uploaded onto the National DNA Database, leading to a match to a profile recovered from evidence in an old case. An interesting case of this type has been reported in the UK media this week, which you can read more about in this article. There are also many examples of individuals being exonerated of crimes they have been convicted of when DNA testing is applied to old evidence samples and shows that they could not have been the source of the sample. A big part of this work is done by innocence projects, originally in the USA but now also in the UK. In the UK many innocence projects are based at universities and involve students working on real cases; you can read some more about this here.

The DNA process and interpretation/analysis of results are subject to the stringent independent review. Whilst the specifics will differ slightly in different forensic labs, all labs will have some form of verification process whereby the results determined by one DNA analyst will be checked by another and this is a legal requirement in the UK. In addition to this, there are various processes that are used to continually check that DNA profiling procedures are working correctly. This includes proficiency testing, and most labs will carry out regular testing of their analysts by checking the results they get for samples with known DNA profiles. Often the analyst will not know they are being tested so that they don’t unconsciously change the way they work. All of the techniques used in the DNA profiling procedure are also validated, i.e. tested with known samples to determine that they are working correctly. In addition, labs who do DNA profiling must be accredited, which means that they are regularly checked and inspected by accrediting bodies to make sure they are carrying out procedures correctly. In the UK, for example, there are fewer than 20 labs who are accredited to generate DNA profiles for loading onto the National DNA Database, and this is to ensure that the data is as reliable as possible. In addition, labs will always use positive and negative control samples to ensure that all of the regents and techniques are working properly, and that there has not been any contamination of samples. Labs have internal processes to check every new DNA profile they create, against every other profile they have ever produced from any case and they will also usually have DNA elimination databases, which contains the DNA profiles of all of their staff and any individuals who may come into contact with evidence samples. This means that all DNA profiling results can be checked against this database to ensure that there has not been any contamination in the lab and all of this is done before any results are reported or send for loading to the National database. Labs also have extremely strict guidelines for anticontamination procedures, from daily/weekly/monthly/quarterly/annual cleaning protocols, to protective clothing to restricted access to the labs. In the DNA process itself, it is a legal requirement for all steps to be witnessed and so staff work in pairs, one as an operator and another watching them to witness as samples are transferred in each stage of the process. The introduction of automated DNA machines further eliminates potential risk of “human error”.

Anne Martin also goes on to talk about the 10 STRs used for profiling and that DNA is not as “unique” as previously understood. In addition, Dino Mora asks about the use of universal DNA databases. Different countries have historically used different set of STR loci, or sets that only partially overlap, but over the last decade countries have reviewed these and there is now a much greater consensus over which STRs are analysed. Until recently, the standard DNA profile in the UK consisted of ten STR regions plus a marker to determine the sex chromosome complement of the donor of the sample, i.e. whether they have two X chromosomes or and X and Y chromosome. This was known as the SGM Plus system, and was developed by the UK Forensic Science Service in 1999. However, in the last few years labs in the UK have moved to new systems. In England and Wales, since 2014 a DNA profile now consists of 16 STR loci plus the sex marker, and in Scotland we moved to a system with 21 STR loci and three sex markers in 2015. Part of the reason for implementing these new kits, as well as increasing discriminatory power by increasing the number of loci, was to bring the UK in line with the recommendations of the European Network of Forensic Science Institutes and the European DNA Profiling Group, who specified a European Standard Set of loci. In terms of sharing DNA profile information more widely among countries, this is a subject of much debate, and many people have concerns about the sharing of DNA profile data between countries, for example due to the potentially sensitive information stored within an individual’s DNA profile, and the wide variation in scientific standards among different countries. Sharing of DNA data is not done automatically, but depends on legal agreements between different countries. For example, several EU member countries have signed bilateral agreements with the United States to share DNA profiling information. Countries who are members of INTERPOL are able to submit DNA profiles to the DNA Gateway, which automatically searches against DNA profiles contributed from 73 member states and returns a result within 15 minutes. Within the European Union, the sharing of DNA profiling information is also carried out through the Prüm Convention, a treaty signed in 2005 allowing EU member states to make direct searches of DNA profiles in national DNA databases of other EU member states. Currently, not all member states are signed up to this agreement, and the UK initially opted out of the treaty due to concerns over the increased chance of adventitious or false matches due to the unusually large size of the UK database. This is exacerbated by the fact that until recently there was only limited overlap between the UK and countries in Europe in terms of the regions of the genome that were tested. This meant that a search could be made under the Prüm Convention with data for only six regions (whereas at the time typically ten regions were tested in the UK), which makes the likelihood of a coincidental match much higher. The newly adopted DNA-17 system in England/Wales and DNA-24 system in Scotland means that there is now much greater overlap with DNA profiles produced in Europe, and so the chance of adventitious matches should be lower. As a result of this and advice from law enforcement agencies that Prüm offers significant benefits for the investigation and prevention of crime in the UK, in December 2015 the UK parliament voted to join the Prüm Convention. This is considered to be much more efficient than current methods of cross-border cooperation through INTERPOL, and will include safeguards against the issue of potential adventitious matches, with the National Crime Agency acting as a gatekeeper for the process. In late 2016, the UK government confirmed that this would go ahead despite the UK EU referendum result in June 2016, although it remains to be seen whether this will be the case.

Ayleesha Buck also asked about databases and how useful DNA is when there is not a match to the database. Often the database is used to try to identify an unknown suspect such as in the case of a “stranger rape” or burglary when the police do not have a suspect in mind. However, where the police do have a suspect they can obtain a reference sample from that individual which is then directly compared at the lab to either include or exclude the suspect, so there is no requirement to compare samples to a national database. Another benefit of the database where the identity of the offender is unknown, is that the database can highlight individuals who partially match the offender’s profile, and so may indicate that they could be a relative of the offender (even if the individual themselves is not on the database). Whilst this is much less common this has been used successfully by the police as an intelligence tool to try to identify an offender.

A promising area of research is in developing more sophisticated tests on DNA that allow the investigator to determine some physical characteristics about the individual who left the sample. If a DNA sample is found at a crime scene and a profile is produced, without a suspect or a match on a DNA database there is very little that investigators can do with the DNA evidence. However, there is now quite a large body of research developing tests that allow more information to be extracted from the DNA sample to help investigators try to identify the donor. For example, by examining the genetic type that an individual carries at certain places in the genome it is possible to determine what eye colour and hair colour they are likely to have, and also what ethnic group they are likely to come from. It is also possible to estimate an individual’s age by looking at a type of chemical modification in their DNA, which changes as they get older. Some of these tests are now so good that they can estimate an individual’s age to within a few years. There is scope for a range of characteristics to be tested for in future, for example there is work being done using DNA testing to determine the face shape of the individual. This is a really fascinating area of research with the potential to have a huge impact on the investigation of crime. One final comment relating to DNA databases when an unknown DNA profile is recovered from a crime scene, but a search of the national and international DNA and fingerprint databases reveal no match. There is very little that can be done at this stage, and often cases will remain unsolved for decades with no DNA match. However, these crime scene profiles will remain on the national DNA database and will be searched against any new profiles that are added. If an individual subsequently comes to the attention of the police, their DNA profile will be added to the database and searched against any unmatched crime scene profiles. This has sometimes resulted in crimes being solved many years after they were first committed; an excellent example of this is the case of Marion Crofts from the UK, and you can read more about this case in this BBC news article.

Lee Scott asked about the minimum amount of blood needed to produce a useful and reliable DNA profile. Blood is extremely DNA rich (DNA is found in white blood cells) and generally provides the best quality DNA results from the smallest samples. Most commercial kits currently on the market are optimised for use with around 0.2-1 nanograms of DNA, or 200-1000 picograms. 200 picograms represents the DNA from approximately 30 cells, and this quantity of DNA can reliably and robustly produce a DNA profile, as long as there are no inhibitory chemicals in the sample, which can be the case in some specific types of samples. Useable, full DNA profiles have been generated from only 10-20 pigograms of DNA, representing only around 2-4 cells!

Mailea Rambeiri and Sarah Burton asked about the testing of Mr and Mrs Ward’s hands for gunshot residue, and why this was not done. In general terms analysing samples for gunshot residue could be useful, and in some case contexts could give you some useful information. However, there are some important limitations of gunshot residue evidence, particularly in this specific case. The first is that in any shooting, particles of gunshot residue are transferred onto surfaces near to where the gun was fired, including skin, clothing, nearby surfaces etc., but they are also lost very quickly. Many forensic laboratories will not accept items for examination for gunshot residue if they are collected more than a few hours after the incident took place, as it would be unlikely to produce any useful information. By the time the police got to Mr Ward it is possible any gunshot residue on his hands would have been lost. The second limitation, specific to this case, is that here we have a situation where two people were shot inside/around a vehicle, and so it is likely that there will be a lot of gunshot residue all over those people and the inside of the car. Mr Ward’s hands could be tested for gunshot residue, but if this is found then it could be explained by him touching his own arm where he was shot, touching Mrs Ward or touching the inside of the car. So, whilst it might be possible to identify gunshot residue, we have to think about whether this would actually provide any useful investigative information.

Kelly Stark and Pete B asked about what cases I have found particularly interesting where forensic biology has played a significant part. That is such a difficult question to answer, but I’ve come up with two cases that I think demonstrate how powerful forensic science can be and how the determination of forensic scientists can lead to convictions in cases that may have otherwise been given up on. The first is the murder of Stephen Lawrence in a racist attack in Eltham in London in 1993, which occurred 25 years ago and was worked on by Strathclyde’s Director of Forensic Practice (see timeline here). After failed public and private prosecutions and a change in the law in England and Wales to allow suspects to be tried more than once for the same crime (the ‘double jeopardy’ legal principle), the persistence of forensic scientists working at LGC Forensics led to the discovery of blood, fibre and hair evidence that was crucial in the conviction of two of the original five suspects in the murder. You can find out more about the case and the forensic evidence involved in this [BBC article] (http://www.bbc.co.uk/news/uk-16257377). The second case is the World’s End Murders, which by coincidence was the first case to be tried in Scotland after a similar change to the double jeopardy law there. In this case, collaboration between a number of different forensic laboratories meant that in 2014 Angus Sinclair was finally convicted of raping and murdering 17-year-olds Helen Scott and Christine Eadie in Edinburgh in 1977. In particular, the work of my colleague Lester Knibb, Geraldine Davidson at Cellmark in England, and Professor Lorna Dawson at the James Hutton Institute in Aberdeen was vital in securing this conviction.

Gwen Boult asked a question about blood stains and brain matter on Mr Ward’s clothing or the car. Both close range and long range gunshots would produce very large forces impacting into blood and so would produce very small blood spatter, less than 1-2mm in diameter, and often in the form of a mist. With longer range shots the force may be somewhat reduced and so the spatter may be slightly larger than with closer range shots, and with closer range shots the gases from the muzzle of the firearm may influence the travel of the blood spots, so the directionality of the spots could be less reliable in determining the origin of the force. However, in general, the blood spatter would be fairly similar, and is likely to be extremely small in size. In addition, a gunshot wound to the head with no exit wound will result in instant death and so does not produce a wound that would bleed a great deal, so there may not actually be a large amount of blood present.

Michelle Fullwood asked about DNA matching of non-identical twins. Non-identical twins, like most full siblings, share approximately 50% of their DNA. However, until recently, one of the limitations of forensic DNA analysis was that it could not be used to tell identical twins apart. In 2014 Eurofins published a paper in which they sequenced the whole genome of a set of identical twins, as well as the child of one of the twins. Out of the three billion letters in the human genome, they were able to identify five genetic mutations that were present in the child and the twin who was his father. This has the potential to allow investigators to distinguish between identical twins in paternity cases, or criminal cases where one of a set of twins is the alleged source of DNA found at a crime scene. The study used a technique called next-generation sequencing, which is a method for very quickly and accurately sequencing a large amount of DNA. Although such methods are currently too expensive to be routinely implemented in forensic casework, the use of these new technologies looks set to revolutionise the way forensic DNA analysis is carried out in future. You can read more about the use of this technique for discriminating twins here.

Gerardo Bloise asks about Rapid DNA machines. These are in use in some forensic labs in the United Kingdom, and can produce results in 82 minutes. However, due to the need for accreditation and validation of the systems and the associated costs, they are not something that are currently in widespread use. There are however, some ongoing trials and research projects for implementing these devices into Police stations for use as intelligence only tools in quickly identifying suspects, in these instances conventional DNA profiling would still need to be performed subsequently so that the findings can withstand the standards required for evidential use in a court of law.

The use of DNA evidence in court brings us on to Gary Lee’s question about stating that the DNA blood evidence “could have” come from Mr and Mrs Ward. When reporting DNA evidence in court the probabilities put forward in relation to the matching of DNA profiles have to be clearly and carefully worded. Whilst the techniques of DNA profiling and the associated statistical evaluation of the results are well established and accepted (and usually go uncontested in court) it is critical to point out that judges and juries may not be able to evaluate this evidence fully, and this is an important point in relation to the presentation of forensic evidence in court. Scientists should communicate the principles behind their science in a manner that can be understood by those who do not have a scientific background, but this can be challenging, particularly with quite technical evidence types such as DNA. The reason the DNA “could have” is firstly that the result is dependent on the match probability calculation for the profile(s) obtained, for example, a full profile with alleles at each loci is more discriminative than a partial profile with alleles only at some loci, but more importantly, we always base our findings on basic scientific principles; we do not have the DNA profile of every individual who is or has ever lived and therefore we cannot say categorically that DNA is unique since we have not scientifically tested this theory and found it to be true. Instead we calculate the match probabilities to be able to place significant statistical value on the findings and say that the DNA “could have” originated from the named individual rather than being definitive since we simply cannot know if someone has or ever will have the same DNA profile at the loci analysed, albeit statistically a low probability.

Barbara K-S has asked about the ethical issues teaching real life cases. As you know the “Murder on the Loch” is based on an old case, but we have changed key details to protect the identities of the individuals. Whether teaching or presenting at conferences it is critical to ensure that no confidential or sensitive information is disclosed. This can be done by anonymising information or alternatively, in some instances we can use information from cases which have been to court and tried, therefore the details are already in the public domain due to news coverage and media reporting. Clearly, there is a still a moral issue about sharing images and confidential information and it is therefore the responsibility of the Forensic Scientist to ensure they are always acting with integrity. Today, many UK cases are covered by the Official Secrets Act 1989, confidentiality agreements and non-disclosure agreements which prohibit the sharing of any information even after trial.

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Introduction to Forensic Science

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