Jurors presented with gruesome evidence, such as descriptions or images of torture and mutilation, are up to five times more likely to convict a defendant than jurors not privy to such evidence, UNSW research reveals.

The finding, from two published mock trial studies, lends support to concerns by the Australian Law Reform Commission that admitting gruesome evidence may prejudice juries by influencing them to make decisions based on emotion or a desire to punish defendants.

"The finding that gruesome evidence can be prejudicial suggests that such evidence should be excluded in court proceedings," says one of the research authors and UNSW PhD student, David Bright. "Gruesome information in the form of pictures or descriptions appears to influence jurors' decisions by increasing the incriminating value that they ascribe to such evidence.

"The results of our research and of other researchers suggest that the prejudicial influence of gruesome evidence on decision making occurs at an unconscious level. Jurors appear to be unaware of the extent to which they are susceptible to prejudice as a result of exposure to this type of evidence."

"Established safeguards, such as judicial directions that jurors should view such evidence in a calm and deliberate manner, probably don't offer sufficient protection to defendants."

Provisions in Australian statutory and common law dictate that gruesome evidence is less likely to be excluded in jury trials. A review by Mr Bright and Dr Jane Goodman-Delahunty of cases that have considered the potential prejudicial impact of gruesome evidence, such as postmortem photographs, reveals that Australian trial and appellate judges are reluctant to exclude such material.

"Australian case law tends to assume that post-mortem photographs, for example, have little or no prejudicial impact on juries," says Dr Goodman-Delahunty, an Associate Professor in the UNSW School of Psychology. "Gruesome photographs have been considered for exclusion by NSW criminal courts on several occasions but in each case courts have held that the probative value of post-mortem photographs outweighed any prejudicial impact on jurors."

During the 1996 "backpacker murders" trial of convicted serial killer, Ivan Milat, the defence team challenged the admissibility of photographs of one of the victim's skeletal remains.

However, prosecutors argued that to connect the murder to other murders and to implicate Milat as the perpetrator, the photographs should be admitted to demonstrate the savagery and cruelty of the murders.

The UNSW research indicates that photographic evidence, irrespective of whether this evidence is neutral or gruesome, can increase the likelihood of conviction, according to Mr Bright. "Admitting gruesome photographic evidence appears to increase the incriminating value that jurors ascribe to prosecutorial evidence by influencing jurors' emotional state."

Media contact: Dan Gaffney, 0411 156 015, d.gaffney@unsw.edu.au