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Drug Profiling – Common Source: what does it actually mean to your case?

September 01 2011

Forensic Science Interpreting The Evidence

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Drugs and Toxicology

The prosecution often allege drugs have come from a common source, but what does this mean, how do they prove it and is it significant?

Drugs such as heroin and cocaine are produced from natural products and contain impurities in varying amounts specific to their manufacture.  The ratio of these impurities to the drug (and/or its degradation product) will remain constant throughout the life of the drug, irrespective of its subsequent cutting.  The use of cutting agents can discriminate later stages of the distribution chain.  The chemical profiling of two drug samples in order to measure these ratios can be very useful, therefore, in determining whether they have a common source of manufacture or distribution.

The term chemical profiling, however, may be used to describe analysis carried out to varying levels of detail.  In cases where a common source is alleged it is important to establish the accuracy and relevance of the chemical profiling results reported.

We have encountered several cases recently where the Crown have mis-represented the significance of the chemical profiling results and one instance where existing analysis which refuted the prosecution’s allegation had not been reported at all!

Case 1:  Two wraps of heroin powder were recovered, one from the defendant and another from his home address and a charge of dealing alleged. The Crown scientist reported that although chemical profiling of the heroin powders showed different purities (42% and 54%) they shared similar chemical components and, therefore, both were from a common source.  On examination we found differences in colour, purity and levels of cutting agent indicating that they were not from the same immediate street batch of heroin powder.

Case 2: Two quantities of cocaine powder were recovered, one from the defendant’s handbag and the other from her home address and a charge of dealing alleged.  The defendant maintained that they were unrelated.  The Crown analysed them and reported both items as pink powder containing cocaine to support their case.  The court subsequently ordered that a more detailed comparison be undertaken but the prosecution scientist stated there was insufficient material to undertake detailed chemical profiling.  On examination we found that the powders, whilst both pinkish, were different in colour and texture and, significantly, the original analysis conducted showed different cutting agents which had not been reported by the Crown! This confirmed that the cocaine powders were not directly related and indeed the lower purity powder could not have been produced from the higher purity powder.

In this case, detailed chemical profiling and the potential common source of the manufactured batch was irrelevant – if the known differences had been reported properly in the first place the issue of whether the powders were related could have been resolved much earlier.

Case 3: In a twist to the normal use of chemical profiling, in a recent heroin import/possession case the prosecution scientist reported that two samples had different chemical compositions and, therefore, were not linked.  The defendant’s account was they were purchased from the same batch but stored under different conditions.  Close analysis of the chemical composition showed that the impurities were in the same ratios and when the percentage composition of drug was added to that of its decomposition product in each of the samples then the samples did indeed match and the defendant’s account was substantiated.

In conclusion, detailed chemical profiling can be a useful tool in assessing similarities between illegal drugs but other information such as colour differences, purity and cutting agents also need to be considered in assessing whether or not two powders are directly related in the context of a case, or whether the common source alleged is actually several steps back in the supply chain.

Author

Sarah Morley

Sarah Morley
BSc(Hons), MSc

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