They almost certainly know Barry did this, but they still have to prove what “this is.” Namely, that Suzanne was murdered by Barry.
Say you know the bike was staged, you can prove Barry staged it, the alibi is garbage, his gps data shows inconsistencies, you can show he lied repeatedly: that still doesn’t prove murder.
Without a body, this case is going to be made up of a ton of pieces. When this happened, I figured we wouldn’t see an arrest before 6 months. It just struck me as that kind of case. It’s different than the Stauch and Berreth cases, which included the dumbest killer alive, and a cooperating witness, respectively.
I have no doubt they’ll get there though, and I actually don’t think they are very far off.