By Dr. Ken Broda-Bahm:
Sometimes characters are important, but never seen. For example, Godot is waited for, but doesn't make it to the stage. In HBO's Veep, the President is often the center of the story, but is never seen or heard on screen. Even in the Charlie Brown cartoons, we hear about but never get to meet the "little red-haired girl." There are parallels in the trial world: The list of individuals who play a role in the stories, told by both sides, is generally longer than the witness list. Of course, for those who are truly key to the story, one side or the other will want them there, yet there are still circumstances -- death, distance, and doubt (about what they'll actually say) -- that can still keep them off the stand.
The legal mindset, as well as the jury instructions, tell us that jurors will base their verdicts strictly on the testimony and other evidence they see, and not the charaters that they hear about, but never from. Those who aren't called, we would like to think, aren't going to be a factor. Not so. Those of us who do frequent mock trials know that when you test only a handful of witnesses, mock jurors are prone to think about those they haven't heard from. And new research focused on the effect of hearsay testimony (Sevier, 2014) indicates that jurors are likely to evaluate absent witnesses as readily as they evaluate the present ones. That finding has implications for the treatment of hearsay evidence, and also encourages us to think broadly about the whole cast of characters in the case drama, and not just the subset called as witnesses.