The cautious approach adopted by scientists to reporting low levels of gunshot residue does not mean the evidence is necessarily inadmissible or irrelevant. The low level of the findings is not determinative as to whether the evidence has probative value. Inconclusive low level gunshot residue evidence found at the scene of a crime or in a getaway car may have probative value if admitted as a component in the body of circumstantial evidence advanced as the Crown’s case to show it is not open to the defendant to say there is an absence of scientific evidence connecting him or her with the crime, provided the jury are given a careful and fair direction as to the use that could be made of the evidence (paras 30, 34–36).

Where there is intervention by firearms officers, who are often contaminated with gunshot residue, the effect of evidence about their presence is that it provides another possible explanation for the presence of low level gunshot residue, in addition to chance and the likelihood of it having been left by a person involved in the shooting, which goes to the weight of the evidence rather than its admissibility. The gunshot residue evidence can be put before the jury in a way which enables them to understand its possible implication as circumstantial evidence. Where the effect of the intervention of firearms officers results in the contamination of the control sample being taken by the scenes of crime officer the gunshot residue evidence can be aggregated with other circumstantial evidence and support the conclusion that the residue was in the car as a result of the person or persons involved in the shooting being present in the car. The gunshot residue evidence is admissible and it is for the judge to direct the jury as to how to approach it in his summing up (paras 12, 46, 48).

The correct approach in summing up is for the judge to make clear to the jury that (i) if they think the gunshot residue may have got into the car by chance or contamination it should be disregarded; (ii) the gunshot residue on its own proves nothing because it is at such a low level; and (iii) whether the gunshot residue can be added to the case against the defendants depends on the jury’s view of the other evidence (para 63).