Indeed, the concern is that jury members may expect a slam dunk in terms of forensic evidence, as seen on TV.
True story: there was one rather naive panelist on our jury who actually argued that the fact that defendant had a criminal record proved that he was innocent--because, having already been convicted of the same crime, why in heaven's name would he make that mistake again?
I patiently explained to her the concepts of career criminals, recidivism, and self-destructive behavior patterns . . ..