This weekend saw the death of Kenneth Perry, thirty-two years after the High Court quashed his wife’s conviction for attempting to murder him. Perry died as he had lived for decades, staunchly maintaining that his wife played no role in several bouts of arsenic poisoning he suffered in the late 1970s. Emily Perry was never retried by South Australian prosecutors, while a further charge for the murder of her first husband laid by Victorian prosecutors was dropped in 1986.

The High Court’s judgment in Perry v R is famous for its bold stand against convictions based on so-called ‘similar fact’ evidence. Because Kenneth Perry maintained his innocence and supplied an alternative explanation for his arsenic poisoning, the Crown’s case against Emily Perry focussed on three other alleged incidents of arsenic poisoning: the death by arsenic poisoning of her first husband in 1961; the  death by arsenic poisoning of her brother in 1962; and the illness of her de facto in 1967, which a forensic witness testified was consistent with arsenic poisoning. Although she was convicted by a jury in 1980, the High Court quashed the conviction at the conclusion of her appeal hearing in April 1982. In reasons for judgment issued eight months later, the Court unanimously ruled that the third incident (where there was no direct evidence of arsenic poisoning and where the de facto eventually died due to a separate poisoning incident) was inadmissible, while half the judges also held that the second incident (where the accused had no financial motive and where the arsenic poisoning may have been self-inflicted) was also inadmissible and one held that all three  were inadmissible. The latter judgment by Murphy J is a textbook analysis of the dangers of ‘coincidence evidence’, such as proof in old cases, disputed forensics and common misunderstandings about improbability.

The Perry case had a further significant legacy in Australian evidence law. Justice Murphy’s conclusion that none of the earlier incidents was admissible was based on his finding that each left open a ‘rational hypothesis’ consistent with Emily Perry’s innocence of the attempted murder of Kenneth Perry. Over a decade later in another South Australian appeal, Pfennig v R, a majority of the High Court adopted Murphy J’s test as the common law standard for the admissibility of similar fact evidence. However, although the current High Court continues to endorse this test, it was swiftly rejected by the top courts of the UK and Canada and is now only the law in Queensland. The remaining Australian legislatures rejected Murphy J’s test either through the enactment of specific legislation or when they adopted Australia’s uniform evidence law. The most recent rejection occurred in South Australia, the jurisdiction where Emily Perry was originally convicted, in legislation that commenced on 1 June 2012, four months after she died at the age of 85.