I think the reality of criminal court cases is that in the vast majority of cases the defendant is clearly and unambiguously guilty. Most criminals aren't smart and aren't covering their tracks. Thanks god the legal system doesn't need to rely on some really smart Lieutenant Columbo to figure out who's done it. Of course there are some more difficult cases but if you pick 10 randomly, you are unlikely to find one. I suspect most juries mostly deliberate about the degree of implications, mitigating circumstances and the severity of the sentencing.