I think that if you believe that this is the criteria by which this case will be decided, you are kidding yourself. It's nice to say the "innocent until proven guilty" stuff because it's the right thing to say and it's interesting to discuss theoretically whether the case has been proven. But after the first few days of the trial this turned in to a case of Brad having to prove that he didn't do it.
As many here have said, it's always the husband in cases like this. The jury knows that too. So, that's the baseline assumption. Then as soon as they heard that there were marriage problems (motive) and that Brad had no solid alibi (opportunity), it became the defense's challenge to prove that he's innocent.
After hearing from Nancy's mother's emotional testimony and seeing photos of Nancy and the kids, the jury is going to want to see someone punished for her murder. As long as it seems likely that Brad did it, they are not going to let him walk just because the DA's failed to prove it. They know that it's not like if they find him not guilty the Cary police are going to say "ok, I guess he didn't do it" and go out looking for someone else. So, if they don't find Brad guilty, Nancy's murder will go unpunished. They are human, they won't let that happen.
It's just like 90% of the people here. Even without a "smoking gun", the only thing that would make them believe that Brad didn't do it is if somehow the defense proved that he couldn't have done it. The onus has been on the defense from the beginning.
As I said, I think that he probably did it and that's going to be close enough in this case.