Electioneering politicians in South Australia have backed a proposal to allow, for the first time, jurors in criminal trials concerning s-x crimes and crimes of violence to hear about “relevant” prior convictions of the accused. Yet overseas examples show it leads to unsafe verdicts because prejudice overrides reasoning.

Premier Mike Rann says the move is “about making sure that juries have all the facts before them”; “this is about doing something for the victims”. The opposition Liberal Party looks set to support the idea.

There have been several studies on this topic over the years, most recently and arguably the most advanced by Cornell University scholars Theodore Eisenberg and Valerie Hans.  Their study, which examined more than 300 jury trials in the US, was published in the 2009 Cornell Law Review.

Eisenberg and Hans reviewed previous studies and these 300 trials and concluded unambiguously that:

“Experimental and real-world data, as confirmed by this study, uniformly suggest that knowledge of defendants’ prior records promotes conviction in close cases, those where one should be most concerned about erroneous convictions.”

In other words, in cases where the evidence is complex or unclear, a jury might be more likely to convict a person rather than give them the benefit of the doubt if they knew the person had committed a similar crime in the past.

The chances of a high number of innocent South Australians being convicted of serious criminal offences if Rann and the Liberal Party have their way is borne out by these frightening findings by Eisenberg and Hans:

“Juries appear to rely on criminal records to convict when other evidence in the case normally would not support conviction. The effect in otherwise weak cases is substantial and can increase the probability of conviction to over 50% when the probability of conviction in similar cases without criminal records is less than 20%.”

This latest body of research is highly consistent with previous work.  In 1995 the Oxford Centre for Socio-Legal Studies in the UK found jurors having knowledge about a person’s previous criminal history can strongly prejudice the case against them. This finding was confirmed last year in a similar study carried out by the same body showing magistrates’ views on defendants change for the worse when they hear about prior criminal history.

So what is driving Rann and the Liberal Party in making criminal proceedings even more difficult for accused persons? Given the empirical evidence against such a move it would seem to be simply pandering to the victims lobby and its many friends in the media.

How can it benefit a victim and their family if the person who committed the crime is still running free in the community while an innocent person has been convicted because the jury, having heard that the defendant had committed similar crimes previously, was likely to have caused this crime?