A third verdict option: exploring the impact of the not proven verdict on mock juror decision making

In most adversarial systems, jurors in criminal cases consider the binary verdict alternatives of “Guilty” and “Not guilty.” However, in some circumstances and jurisdictions, a third verdict option is available: Not Proven. The Not Proven verdict essentially reflects the view that the defendant is indeed culpable, but that the prosecution has not proven its case beyond a reasonable doubt. Like a Not Guilty verdict, the Not Proven verdict results in an acquittal. The main aim of the two studies reported here was to determine how, and under what circumstances, jurors opt to use the Not Proven verdict across different case types and when the strength of the evidence varies. In both studies, jurors were more likely to choose a Not Proven verdict over a Not Guilty verdict when the alternative was available. When evidence against the defendant was only moderately strong and a Not Proven verdict option was available (Study 2), there was also a significant reduction in the conviction rate. Results also showed that understanding of the Not Proven verdict was poor, highlighting inadequacies in the nature of judicial instructions relating to this verdict.