One stereotype of juries is that they often make judgments based on their own speculations and amateur detective work–that they move far beyond the evidence in the trial to interject their own suppositions and biases. I fear that this comes, in part, from the cultural memory of a powerful scene in 12 Angry Men, where a juror reveals that he’d done sleuthing on the sly to procure a copy of an allegedly unique murder weapon.
In truth, juries more commonly stick fast to the evidence. When they ask judges questions during their deliberations, it’s often requests to get instructions clarified or evidence shown to them again, as in the case of the recent Baltimore jury that reexamined a bullet entered into evidence. As that article noted,
Jurors must almost invariably rely on evidence presented during trial — and submitted to them after closing arguments — as well as on their memories of testimony and any notes they might have taken.
Even this gets reinterpreted by jury critics into a belief that there is now a ‘CSI effect‘ in juries, whereby jurors come to demand a level of direct evidence comparable to that they see on TV. To quote from a USA today article on the subject,
Prosecutors, defense lawyers and judges call it “the CSI effect,” after the crime-scene shows that are among the hottest attractions on television. The shows —CSI and CSI: Miami, in particular — feature high-tech labs and glib and gorgeous techies. By shining a glamorous light on a gory profession, the programs also have helped to draw more students into forensic studies.
If one really wants to learn about how juries reach verdicts, check out Neil Vidmar and Valerie Hans’ The American Jury: The Verdict. It’s a sober account–and one that helps exonerate the jury from the more dubious charges against it as a serious deliberative body.