The phrase "...beyond a reasonable doubt" comes to mind. I would hope a jury involved in such a case would be more reasonable about actual hard evidence, but I hear that juries are selected for emotionality and not rationality. I would hope that the judge in such a case would be more reasonable and demand some actual evidence.
Such is the case in a fearful populace, and one that demands vengeance over justice. I appears as though something bad happened, so someone must pay and ... here's a magic forumla with missing variables that says you might have done it so ... GUILTY.