I'm certainly no expert on juries, as was evident from my last trial, but I think that most who wind up serving are there because they want to be. Sure, they've been summoned but it's all too easy to get out of it. I've served twice and both times, the attorneys on both sides wanted me on there. Both were criminal cases and both sides knew that as an attorney, I should be better prepared to take emotion out of it and decide:
A. Did the prosecution prove the elements of the crime, or..
B. Did the defense prove otherwise or that there's reasonable doubt that they met the elements.
JR can tell you far better than I can because criminal defense is something I only did for a short time. Criminal prosecution pretty much boils down to intent and proving the elements of the crime as defined in the Code. Before and during voir dire, you have to do your due dilligence to try and get jurors who you perceive to have the ability to look at things and make their decisions based upon the evidence and the jury instructions given. Not based on emotion. Except in the case of the Casey Anthony trial, where the prosecution I'm sure knew full well that they couldn't meet their burden of proof but wanted jurors to look at the beautiful little girl in the picture and in turn, hate her mom.