Fragmentation of cases may mean missing part of the puzzle

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Current concern among forensic scientists is the ‘fragmentation’ of cases.

What this means is different exhibits from a case are sent to different laboratories and no one forensic scientist maintains an overview of what is happening. Such cases are managed by the Police rather than forensic scientists and the argument is that the Police may not fully understand the importance of the results or may be more swayed by need to restrict the spend rather than the need to produce a full set of results. This concern was highlighted in the 2013 Science and Technology Committee report ‘Forensic Science‘ and in a case report from Forensic Access.

I also had a good example of what could occur in such a case in my work recently. I have been working on a case involving hair testing. I was asked to review the data from some tests and interpret them with regard to the initial reports prepared by a medical examiner and another toxicologist.

Hair sample

We all agreed the results were fit for purpose and produced satisfactorily. We did differ slightly in our interpretation, which meant we were asked to go in front of the hearing to discuss this. The gist of the disagreement was whether the results found were due to use of cocaine or whether the results could be explained by another reason. I argued that given the low levels (even though I do not believe you can say how much has been used from the level reported, more to come on that shortly) and a negative body hair sample it could be argued that the sample was positive due to external contamination of the hair. The pattern observed fitted nicely with published papers, particularly the paper by Romano et al which reported external contamination may be detected for at least 10 weeks after occurring. They also showed the results from a single test would then not be distinguisable from those found in genuine users.

On the morning of the hearing however we discovered a new piece of information, one which the Police in charge of collating the evidence had not seen as important. That information was that the first sample analysed showed ‘significant evidence of contamination of the hair’. Prior to testing the samples are washed to remove any drug on the outside. In this case the washes were analysed and found to contain significant amounts of the drug, enough that the testing company thought this was the explanation for the finding. The Police didn’t understand this and ordered another test from another laboratory who did not see the first results, which came back positive. However, if contamination occurs the drug is seen to get incorporated into the hair and remain there even after washing. This could mean subsequent tests remain positive even though the drug has never been used.


Whilst not being an example of fragmentation exactly, what it illustrates is that Police are not always in the best position to evaluate scientific evidence and that all experts being asked to work on or comment on a case should be given access to ALL of the information available.


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About Dr Tom Bassindale

Dr Tom Bassindale is a forensic scientist, and the founder of We Are Forensic. He is currently the subject lead for chemistry and forensic science at Sheffield Hallam University. He's managed hundreds of forensic toxicology cases, and is an experienced court witness. He has specialist expertise in forensic toxicology and drug testing in sport. And yes... he watches CSI.