JMO, I think DeWine's reference to bizarre means the jury (and the rest of us) will be surprised at how stupid and selfish the Wagners were in planning and executing these horrific murders. I don't think there will be any doubt who did it, but there will be a lot of people wondering why they did it. IIRC, DeWine said there will be things you hear that will make you shake your head.
For example, the whole concept of the W's getting ideas and inspiration for planning the murders from the "Boondock Saints" movie is pretty unusual. When I first read about the movie, it was a real "WTH, are you kidding me?" moment. Believable that they did it? Yes. Being really stupid and disconnected from reality by doing such a ridiculous thing? Also yes.
As someone else here questioned (paraphrasing) "When the family is sitting around the dinner table planning how to kill 8 people in their homes, doesn't even one of them stop and think "maybe this isn't a good idea".