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Photo of Dr Bill Tilstone

Ask Bill

Please post your questions for this week in the comments section. At the beginning of next week, Dr Bill Tilstone will respond to the most interesting, useful and/or popular questions. Please ‘like’ questions posted by other learners if you are also interested in having these answered.

Thank you for all your questions. Here are Bill’s responses to your ‘most liked’ questions:

Fact and fun, and the perfect crime
We had some more posts on the lines of “what do you think of TV programs that feature forensic science?” The answer is the same - they are made to entertain and most of them do that well while doing the science poorly, for example instant DNA results, and working in what would be unacceptable lighting in a real lab. The same as with many of you, I like a good mystery (personal favourites are “Scandi-noir” like The Killing, Wallander, and The Bridge), but if you want to see something realistic in regards to forensic science there is nothing better than the BBC’s History Cold Cases series. You can still catch it on YouTube. There are some others that are more factual and less sensational than the standard fare - Ryan Merriweather posted some interesting material from a series on the Tru TV channel (in the US).

Some of you showed an interest in how to commit the perfect crime - hmmm! The scientific answer to ‘how to do it’ is that I don’t know - if I did, it would not have been the perfect crime. I realise that the question was asked in fun (or I hope it was - the first rule of getting away with it is not to be suspected, so those who asked better lead blameless lives from now on), but the answer is very much relevant to some of what we have been discussing. In week 1, when dealing with responding to an incident we made the point that we don’t know what happened, and we come back to this in week 6. It looks like you are all enjoying “Murder by the Loch” which is good to know. But don’t lose sight of the fact that it is there to aid your learning, and the step-by-step development of an account of what happened is accurate. (You may recall the Body in the Woods case in week 1 where you saw the same thing in another real case). There are no short cuts and there will always be “noise” amongst the real data. A related question was “how often do cases develop into side shoots?” Not all that often but it does happen, probably more frequently in serious crimes.

Field drug testing
There were lots of questions and comments about field drug testing/presumptive tests/TLC and their scientific and legal reliability. There is no absolute answer to the legal reliability question as this is up to the lawyers and social acceptability. I answered some of the questions directly, but in summary, drug analysis in the very considerable number of simple possession cases imposes a huge burden on forensic science resources. Field testing coupled with giving the accused the right to ask for a definitive laboratory test provides a solution that simplifies the whole process, saves resources, and protects the rights of the accused.

A general comment arising from this and other questions posted, is that what the forensic scientists do in drug cases is determined by the laws that apply in the relevant jurisdiction, and the way that prosecution and law enforcement apply these laws. For example there was a question about whether Dougan and Branks would be charged - the forensic evidence is there but what charges would be laid if any is up to the prosecutor.

The “laws that apply in the relevant jurisdiction” is also the answer to the question on why there is a difference in how possession is treated compared to dealing. In general, there is a trend towards lessening the penalties in cases where someone is in possession of small amounts and clearly for their own personal use, and increases in those for dealing.

Finally in this set of questions: where does the pure material used as reference standards come from? It is made under licence from the authorities.

Drugs and the Internet
Given this is an online course, it’s hardly surprising that there were questions about the Internet and drugs.

The general answer is that the Internet is a powerful resource for information sharing, whether between agencies such as INTERPOL and UNODC for legitimate policy and intelligence reasons, or the “Dark Web” including Silk Road and its successors for crime-related ones. A related issue is the Web market place for prescription drugs. It is easy to discount this as being nothing to worry about on the grounds that they are medicines not junk, but there are very good reasons why supply of these drugs is restricted to prescriptions from registered medical practitioners and dispensed by registered pharmacists.

Detecting drugs in the body
This is the discipline within forensic science that is known as “Toxicology”. We don’t deal with it here, but it is used in investigation of deaths due to poisoning, in control of doping in sport (athletics and horse racing for example), and in some criminal situations (acting under the influence of a drug as causal or mitigating circumstances, and driving offences for example). The analytical problems are much more complex and demanding than for the materials encountered in drugs of abuse. The amounts present are typically between a thousand and a million times less than in drugs cases, and most drugs are removed from the body by being converted (at least in part) into a related chemical. These metabolites, as they are called, are obviously similar to the parent drug and can make its specific identification and quantitation very difficult.

A related question was why do different drugs have similar effects / different effects? This is a good question and related to the trends in manufacture of new medicinal and illicit drugs. At its simplest, the action of a drug in the body arises from part of the molecule binding to a complementary site in the target organ (think back to the base pair binding in DNA). These sites are called receptors. Any drug that has a chemical grouping that fits the receptor will produce a similar action (provided that the rest of the drug molecule doesn’t get in the way either physically at the receptor site or by preventing the whole molecule getting into the part of the target organ where the receptors are located). Medicinal chemists are trying to make drugs that are better fits to the receptors that are responsible for the desired therapeutic effect and poorer fits to receptors responsible for side effects. Illicit drug chemists are trying to make drugs that are chemically different to those on the list of controlled substances but that interact with the euphoria-inducing receptors.

Not all drugs work this way though. Some act because of a more general physical or biochemical interaction, for example glue sniffing and alcohol.

Drug deaths
Setting aside issues of breaking the law, and going back to “Drugs and the Internet” I would never buy a prescription medicine online for reasons of safety - you have absolutely no objective proof of the authenticity of what you would get. Likewise with street drug: you have no control over what you get, and every reason to doubt its authenticity. Some drug deaths are simple overdose but far too many are because of lack of control of what’s in the packet - the amount of drug and the nature and amounts of all the other “stuff”, and you are susceptible to problems being introduced at each step in the supply chain.

Non-drug questions
There were some good questions this week that were not about drugs.

Do forensic scientists specialise in one field?
Today most are highly specialised. This was hotly debated a few years ago, with some people concerned that the passing of the generalist meant that there was no real over-view of cases, and potentially valuable evidence was in danger of being missed because the specialist was unaware of its presence or importance. However, there is no way that a generalist could deal with DNA analysis and evidence, or indeed a complex drug case with liquid chromatography/mass spectrometry as the key analytical procedure. This takes us back to Week 1 and John Cockram’s “conductor of the orchestra” concept, moved from the scene into case managers in the laboratory.

If someone received my blood in a transfusion and committed a crime … would biological fluids from the scene result in the police knocking on my door?
No, your DNA will be swamped by that of the recipient.

Would the gun still have finger prints on it after being in the water?
This is not possible to answer definitively. It may have been cleaned, the shooter may have worn gloves, currents could have washed off water-soluble sweat, for example.

Not noting the registration of Dougan’s car is quite a serious slip up
Yes, and the two officers had to make amends

What, if anything, was recovered from the gun?
Nothing

When should defenders raise a challenge to forensic evidence?
Do defenders obtain the underlying notes and reports of the forensic analyst?
It is the responsibility of the defence to thoroughly test all the evidence that could be used against them. Given the challenging forensic evidence involves finding an Expert, reviewing notes, and possibly new or repeat testing, “sooner rather than later” is the best answer.

With what frequency, in reality, do such multi-disciplined forensic investigations occur in the UK?
Not all that often but always best to keep and open mind.

Ethnicity
What if the parents were of different ethnic group, what would be the child identified as? This is from Week 3 and DNA. It is an excellent question that I’m sorry I missed first time. Ethnicity and STR allele population data is very complex. “Ethnicity” is essentially a social matter and there is no specific “test”. Part of defining an ethnic group is a shared homeland and culture, which means that members of the group will tend to marry people from within that group. Hence rare STR alleles will remain rare and common ones will remain common within the group. That’s why we want to know the population frequencies of the STR alleles within specified ethnic groups. In the case you describe, assignment of ethnicity will be up to the parents (and later to the grown-up children), and not decided by their STR profiles. I am outside of the mainstream thinking in forensic science in regard to ethnicity and DNA population data - it’s good to know and have available if asked, but to me the relevant population is the one that had the opportunity to have committed the crime which may not be one that fits an ethnic categorisation. I’d prefer to see DNA data expressed in terms of the overall population frequencies with a rider that these are averages and may not be an exact measure of what would apply in the case. But as I say, this is a bit of a maverick position.

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This article is from the free online course:

Introduction to Forensic Science

University of Strathclyde