2.5 Hearsay

Experts can use wider sources of information to draw their conclusions than standard evidence. This means that they can often draw on material that would normally be treated as inadmissible hearsay to support the inferences they draw. For example, in the case of R v Abadom,^{Footnote 12} the accused was charged with a robbery during which it was alleged he had broken a window. Fragments of glass were found on a pair of shoes taken from his home, and an expert was called to give evidence that the glass taken from the window and that from the defendant’s shoes had the same refractive index (a measure of how light rays are deflected by glass, and which provides a characteristic ‘fingerprint’ for different types of glass). The expert referred to Home Office Central Research Establishment statistics revealing that the particular refractive index occurred in only 4 per cent of glass specimens examined by them. He therefore concluded that there was a very strong likelihood the glass on the shoes had come from the broken window.

Figure 7 Broken glass

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A photograph of an old wooden door or window frame inlaid with textured glass panel. The glass panel has been broken by an impact, leaving cracks in the glass emanating from the impact point. Some of the glass around the impact point is also absent.

Figure 7 Broken glass

Figure 8 Refraction

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A top-down photograph showing light refracting through a glass block. A beam of white light shines from left to right through a rectangular-shaped block of glass. Where the ray of light meets the glass, it is refracted upwards. Where the ray of light leaves the glass, it is refracted downwards. As a result, the ray of light exits the block of glass with a path parallel to that which it entered the block but refracted at a higher point.

Figure 8 Refraction

The defendant appealed against his conviction on the basis that the refractive index evidence was inadmissible hearsay. The Court of Appeal held that the expert had been entitled to use such material in forming his opinion, just as he was entitled to use other work in the field, including unpublished work. It was to be used by the court to weigh the cogency and probative value of the opinion rather than as evidence in itself and, therefore, did not infringe the rule against hearsay.