A poor quality covert recording from an Australian murder case, along with the police transcript used in the trial but later shown to be inaccurate, are used to explore general issues regarding this increasingly common type of evidence. Two experiments were run, in which participants heard an excerpt from the audio, first with no transcript, then with suggested and alternative transcripts. In Experiment 1, they were given no contextual information, while Experiment 2 started with a background story about the case and the issue the recording was intended to resolve. Results indicate that background knowledge of a case can dramatically increase listeners' acceptance of a police transcript, even when the transcript is manifestly inaccurate. It is suggested that such contextual priming may affect not just juries but others involved with the trial, and recommended that police transcripts be treated with more caution than is currently common with Australia's 'ad hoc expert' rules.

This article describes an experiment designed to explore the effects of 'priming' (i.e. being exposed to a suggested interpretation of an audio signal) on how juries perceive disputed utterances in poor quality recordings used as evidence in legal cases. Using the actual disputed utterance from a real case, the experiment tracks how participants' perception of its content changes as evidence about the case is gradually revealed to them. At a certain point, participants are randomly divided into two groups, each receiving parallel but slightly different evidence. Results indicate the dangers of priming may be considerably greater than is sometimes recognised, and unlikely to be overcome by a mere caution from the judge. They also indicate that participants' propensity to consider the defendant guilty may be based on judgements of his trustworthiness influenced by initial impressions of his style of speech, rather than on objective evidence presented to them.