Hey Card, you have to assume DPD has their reasons to let her go. They might be giving her rope because they don't have enough at this time. There is simply no way to know what they are thinking without being a part of this investigation.
Despite my thoughts that BD was in the jeep during the commission of this crime, I have to allow that DPD has more video footage of the jeep - and possibly the actual crime - that they have not publicly released. That footage may show only one figure in the jeep, or more. But I think we can surmise if they could for certain place BD inside the jeep, she'd be locked up.
As for how we know she was involved? Basic deduction and extrapolation. IMO. Coincidences do happen, but it's very unlikely that a heartbroken and jealous woman, obsessed with the new relationship of her ex boyfriend just happens to borrow a vehicle from a friend, only to lend that vehicle to a new friend who just happens to use it in commission of a crime against the new girlfriend of the old boyfriend.
See, even that sentence is so convoluted that it defies logic that BD is not involved. What makes sense is that BD told CC her troubles and the two hatched a plan to hurt Kendra Hatcher in some manner. BD borrows a vehicle - because she certainly won't be caught using her own - and she uses CC (at least as an accomplice) because if CC is the driver (as well as a new friend RP wouldn't recognize), there would be virtually no way to tie BD to the crime.
The last thing I can think of is this: Any time someone is murdered, it's standard procedure to examine the relationships closest to the deceased. You check husbands, boyfriends, exes, co-workers, casual acquaintances - and you widen the search grid to include the relationships of those intimately involved with the deceased. This is how we quickly got to BD. I don't think she'll be free for long.
