Most criminal cases are circumstantial cases. That's because anything outside of a confession, or eyewitness, or a videotape of the murder is, by definition, circumstantial.
That said, there were some important facts mentioned during opening statements:
1. Nancy's running shoes were found in the garage on a shelf, right where she left them. And no other shoes of hers were gone, so she didn't use a different pair of running shoes. The obvious conclusion is that she was not wearing shoes on her feet when she left (or was taken out of the house). And when her body was found, there were no shoes on her feet or anywhere in the vicinity.
2. Brad washed Nancy's dress from the party the night before. He claimed there was a stain on it. No other person saw such a stain.
3. Brad was doing many loads of laundry, including Nancy's laundry the morning she went missing. This is counter to the norm.