R v Keir

The appeal before the Court was against a conviction for the murder of Jean Keir, the appellant's wife, by the Crown. The appeal centred on the trial judge's handling of DNA statistical evidence and its implications on the reliability of identification evidence. The Court was tasked with determining whether the trial judge's directions to the jury regarding the DNA evidence were adequate and whether the conviction should be upheld or quashed.

The central legal issue was whether the trial judge's summing-up on the DNA statistical evidence correctly conveyed its significance and whether the judge's failure to correct the prosecutor's fallacy warranted a quashing of the conviction. The DNA evidence indicated that the bones found at the excavation site were 660,000 times more likely to belong to Jean Keir than to any other person in the Australian population. However, the trial judge's summing-up did not clarify that this ratio did not mean there was a 660,000 to one chance that the bones were Jean Keir's; instead, it left the jury with the impression that such a high likelihood ratio supported the identification of the bones as Jean Keir's. This misunderstanding of the statistical evidence by the jury is known as the prosecutor's fallacy.

The Court found that the trial judge's summing-up had not corrected the prosecutor's fallacy, which significantly affected the reliability of the identification evidence. The judge's directions did not adequately explain that the high likelihood ratio did not equate to a probability of the bones being Jean Keir's. Instead, it should have been interpreted as supporting the hypothesis that the bones were from a child of Christine Strachan and Gaspar Baan. The Court concluded that this error in the summing-up meant the conviction should be quashed due to a substantial miscarriage of justice.

The Court quashed the conviction and ordered a retrial, emphasising the importance of correctly explaining statistical evidence to avoid the prosecutor's fallacy and ensuring that juries understand the true implications of such evidence in criminal trials.