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Ask Penny

Please post your questions for this week in the comments section.

Penny will select the most liked/interesting questions and publish her response to these on this step by Wednesday of week 6.

Firstly, thank you very much for all your excellent questions and comments again this week, I hope you are enjoying the final week of the course, bringing together all of the scientific evidence we have looked at as the case has unfolded. There were some really interesting questions this week, and I also noticed some late questions that came in for the Week 3 ‘Ask Penny’ step so I picked a couple of those up as well.

Given that last week was looking at the analysis of illicit substances, most of the question related to drug analysis. Crawford Thomson asked about drug profiling and whether there is a central body that coordinates this, and Trevor Wood was interested in this as well. In the UK, forensic service providers all have their own drug testing labs and these will all have the capability to do drug profiling. However, drug profiling is not actually done very often as it is very costly, and usually the key issue is just to identify an unknown substance as being a specific controlled drug. This is done using presumptive testing and then confirmatory testing such as GC-MS (gas chromatography mass spectrometry) or TLC (thin layer chromatography). Drug profiling would involve more detailed chemical analysis to determine the components present in the substance in question and to estimate the amount of each component (e.g the drug, cutting agents, impurities). This can be useful in linking different batches of drugs together, and also in linking drugs to a production site/lab. For example, a sample of heroin might also contain diamorphine, paracetamol, and caffeine, and potentially also things like mannitol (a sugar) or anti-fungals. In terms of central coordinated databases of drugs, forensic providers maintain their own databases and regularly make this information available to police, documenting the different types and quantities of drugs found in a given time period. There are also some projects collecting data to monitor seizures of different types of drugs when recovered in relatively large quantities, and these can be used for intelligence purposes.

Related to this, Peter Breeden asked whether the brand of a cutting agent such as baking powder or talcum powder could be identified to assist in linking batches of drugs together. The answer is that food/medical substances like baking/talcum powder are tightly regulated and have to meet very strict specifications, so the chemical structure of these types of substances would usually be the same regardless of manufacturer. Detailed chemical analysis of these types of cutting agents would therefore not provide additional useful intelligence information.

Maggie Owen asked how often it is possible to determine the origin laboratory of drugs seized and how long these types of drugs investigations take. The majority of drug testing done in forensic laboratories is not done to identify the origin lab, the majority of the work done by these labs is to identify what drug someone was in possession of. Linking to a source lab is therefore relatively rare, and the forensic analysis part of drugs investigation is often completed very quickly. However, if the chemical structures produced in different labs are different then they can be differentiated using chemical analysis and so this can be a very powerful method.

Francis Mitchell asked about the recording, documentation and record trail associated with suspected illegal substances recovered from crime scenes and the answer is that these types of samples are subject to exactly the same procedures for maintaining the chain of custody/continuity of evidence as any other evidence type and would therefore be treated in exactly the same way as any other evidence recovered from a crime scene.

Adrian Bradshaw asked whether it would be standard for the police/prosecution to request that the forensic laboratory test the purity of a drug. The answer is that it would depend on what type of case it is-if the police are only charging someone with possession of a drug then the purity would not be important and the forensic analysis would simply involve identifying the drug. However, if someone was being charged with supplying a drug, then the purity would be tested in order to estimate the street value of the sample seized, and this could influence a sentence or fine later on.

Daniel Kraus asked about how Fentanyl and Carfentanyl are dealt with in the UK. These are highly powerful opioids, may thousands of times stronger than diamorphine, and they are increasingly being found in heroin samples. A drugs analyst colleague tells me that due to the strength of these drugs, whereas police officers might normally carry out basic drug testing at a scene, if a sample is suspected of being/containing heroin they will now tend not to do any testing on the sample but send it straight to a forensic drug lab for analysis. This is to reduce the risk to the officers, by sending the sample to be tested in a forensic lab with antidote facilities, in case someone was to accidentally come into contact with the sample.

K S asked what the smallest quantity of a substance is that can be detected in drugs analysis and the answer is that most labs have very sensitive instrumentation that can detect substances at a few parts per million, if set up correctly. Even the instruments used at airports to detect drugs can detect substances at a few hundred parts per million.

K S also asked about the pharmaceutical industry, and this relates to a couple of questions that were submitted about prescription drugs, from Janet Alcántara and Patience Usman. Our course didn’t cover prescription drugs, but that doesn’t mean that these drugs are not of interest to forensic laboratories. Forensic labs will regularly analyse samples of prescription drugs, if requested by the police. This might be because the identity of some tablets is unknown and the police want to know what they are, or because the suspect doesn’t have a prescription for the drugs. In addition, many prescription drugs are also controlled, so they can be possessed with a prescription but are classified as controlled, e.g. in the UK diazepam is a drug that can be issued with a prescription but it is also a Class C controlled substance. There is also a pharmaceutical database containing information about prescription drugs that can be used by forensic labs to identify unknown samples.

Related to these questions, a major issue in forensic drugs analysis in recent years has been the analysis of ‘new psychoactive substances’, previously known as ‘legal highs’. These terms refer to chemicals that used to be legal, but produced similar effects to illegal drugs such as cannabis, amphetamines and cocaine. These were produced with the aim of avoiding the laws controlling the use of illicit substances, which in the UK is the Misuse of Drugs Act (1971). For example, synthetic cannabinoids are a group of chemical compounds that mimic the effects of cannabis. This is because they are synthesised to have structures that allow them to bind to the body’s cannabinoid receptors. The drugs originated in the late 19080s to early 1990s, by chemists who understood how these receptors were bound by the active ingredient of the cannabis plant, ∆9-tetrahydrocannabinol (∆9-THC), which produces the ‘high’ associated with this drug. Synthetic cannabinoids were therefore produced to imitate this effect, by binding the cannabinoid receptors in a similar way. The use of these substances increased hugely in the last decade or so, particularly in Europe, as the chemicals involved were not controlled or regulated by law. In addition to this, very often as forensic drug analysts became familiar with the chemical structure and nature of one legal high, and therefore were able to test for it, the drug producers would adjust the chemical structure of the substances slightly so that the drug’s effect remained the same but the chemical was undetectable in standard drug screening tests. This, in combination with a rise in incidents of poisoning and the number of fatalities, led to an increasing need to regulate these drugs.

Controlling these substances has been very difficult around the world, as no countries had laws to regulate them. However, in the UK, this changed in 2016, when the Psychoactive Substances Act came into force. This law is a blanket ban on the production, distribution, sale and supply of these substances, and these activities are now punishable by up to seven years in prison. Legal highs are added into the list of banned substances as they are discovered, after forensic drug analysts have determined the chemical structure of the substance, and the health risk posed by the compounds has been assessed. However, our pharmacological understanding of these substances is still very limited, and this has slowed progress in identifying new psychoactive substances. New substitutes for legal highs evolve at such a rapid pace that is difficult for the authorities to keep up with, and the drug producers are generally always ahead of the law. If you would like to read more about legal highs, this BBC article gives some more information about them, and this article discusses the introduction of the Psychoactive Substances Act in 2016.

Finally, I wanted to address the really interesting issues put forward by Dana Murray about the presentation of forensic evidence in court. You are absolutely right that science can make significant contributions to the investigation of crime, but that this is of no use unless the science can be effectively communicated in court. Forensic scientists have a responsibility to the court to explain their evidence-and what it means-in a way that is clear and easy to understand, even if someone does not have a scientific background. This can be very difficult, particularly when complex technical concepts have to be explained, and this has caused problems in court cases in the past. Forensic scientists therefore go through a lot of training in how to write clear and concise reports, without using scientific jargon, and these reports usually contain a technical section explaining the techniques used in the analysis of evidence in lay terms. Scientists also go through rigorous training in how to present evidence in court, and how to ensure that the jury can understand their evidence and are not unduly confused or influenced by technical jargon. This should therefore allow the jury to make an informed, unbiased decision about the evidence and what it means.

As I said earlier, I also picked up a couple of questions from the previous Week 3 Ask Penny step that I missed. John Dew asked about whether DNA testing for estimating the ancestry of a suspect is helpful in most cases, and the answer is that it isn’t used in many, if any, cases. Standard DNA profiling tests don’t reveal very much, if anything, about the ancestry of an individual, so a more specialised test such as a mitochondrial DNA or Y-chromosome test would need to be done to generate information about the suspect’s origin. The other thing to consider is that these tests provide information about an individual’s genetic origins, not about their geographic origins, and these may be different.

Alan Percival asked some questions about STR testing, firstly whether particular STRs are targeted and the answer is yes. All commercial STR testing kits target specific known STRs at known positions in the genome (usually on different chromosomes), and in fact a lot of the same STRs are targeted in different kits as they are well-known and well-characterised. In terms of the structure of the STR in the DNA, say for example an individual has a genotype of ‘12,14’ at a given STR that is found on chromosome 15. Every individual has two copies of each chromosome, one inherited from their mother and one from their father. That individual therefore has 12 repeats of that STR sequence on one of their copies of chromosome 15, and 14 repeats on the other copy of chromosome 15. At the sequence level, either side of the STR region the two copies of the chromosome will have (usually) the same DNA sequence, and then within the STR region the sequence differs in that there are two additional repeats of the core sequence on one chromosome. For example, the core sequence of the STR might be ‘GATC’, so on one chromosome the individual has ‘GATC’ repeated 12 times, and on the other repeated 14 times.

I also wanted to answer the question that Cathy Alderson asked in Week 3, about issues around submitting DNA samples for analysis through genetic genealogy sites, for looking at ancestry, such as Family Tree DNA, 23andMe, and Ancestry. I wasn’t sure of the answer to this, so I got in touch with colleagues at the University of Strathclyde who teach on the MSc in Genealogical, Paleographic and Heraldic Studies, including Tahitia McCabe who is Lead Educator on the FutureLearn MOOC ‘Genealogy: Researching Your Family Tree’. In general, my colleagues seem to think that these sites are secure and well-managed. Just like any company with an online presence, genetic testing sites need to maintain online security, so if you trust companies like banks and utility companies with your data then there is no reason not to trust genetic testing sites. The privacy settings on these sites is controlled by the person submitting the sample to be tested, and you have to give active consent for your sample to be passed to third parties or used for research purposes. Most of the big companies have very open Terms and Conditions that you can check you are happy with before proceeding. Samples are anonymised and given an alphanumeric code for identification, so your personal information will only be linked to that via the code. The type of analysis done depends on the type of test being taken, but tests generally include either STR analysis, or ‘single nucleotide polymorphism’ analysis, which looks at mutations at single ‘letters’ in the genetic code. These tests can be carried out on different parts of the human genome, including the sex chromosomes (X or Y chromosome), the autosomes (chromosomes other than the sex chromosomes) or mitochondrial DNA (from the mitochondria, which are small structures in human cells that produce energy, and have their own genome). In terms of who processes and analyses the data/information received from the laboratory, all of these sites employ qualified geneticists and laboratory staff, which is very important when you consider that a lot of the tests being carried out utilise cutting edge technology and analysis methods. The name of key staff at the organisations can usually be found on their websites so you can check this out for yourself, e.g. Family Tree DNA, Living DNA. If you want to find out more about genetic genealogy, the International Society of Genetic Genealogy Wiki is a good place to start, or you can sign up on the waiting list for the Genealogy MOOC above, which should be running again soon!

Finally, in answer to Kathryn Merrett’s question-yes, they did find out what happened-see below for information about the big reveal!

All that remains now is to say that I hope you enjoy the rest of the material in Week 6. The video revealing what really happened will be made available at 16:15 GMT this Friday, 17 November, and we are asking you to vote up to 16:00 GMT on Friday for whether you think Mr Ward is guilty or not guilty. We really hope you will take the time to vote, and we would love to see lots of responses. I would also encourage you to vote according to your analysis of the evidence, and not on your gut feeling. This week we have been looking at a logical system for bringing together evidence and analysing it and thinking carefully about what it means from a scientific point of view. You should therefore focus on the science, work through it all logically and base your decision solely on what the evidence tells you. I really hope you have enjoyed the course, it has been a real pleasure interacting with you and reading all your comments and questions. I have really enjoyed seeing how interested you have all been in the case, and how much discussion you have had about it each week. Thank you very much for joining us for the Introduction to Forensic Science MOOC, and don’t forget to cast your vote before 16:00 GMT this Friday!

Best Wishes,


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This article is from the free online course:

Introduction to Forensic Science

University of Strathclyde