Excellent sum-up of all the relevant points.. and what it says to me is it sounds like the police think (they might say know) that the accused deliberately ran her down with a lethal result, and then moved her body away somewhere and hid it. And then I'd say went on about his business as usual.
I mean, what else could it be, considering the accident reconstruction expert witness inclusion along with the blunt statement by the police that it was not a hit and run. I can't think of any other possibility... if, that is, a hit and run means what I assume it does, which to me is when someone hits a person with a vehicle and runs away, leaving the injured person or their dead body where it is.
And if all this is correct, then it probably also must mean that it was all caught clearly on video. I reach this conclusion because of the mention of, as
@Spectrix above put it, "copious amounts of CCTV" along with the fact that they were confident enough in the truth of their theory to have kept the accused locked up all this time, despite him having no known ties otherwise to the victim. And I feel like this is bolstered by the fact that, as
@Trooper above points out, the accused has never applied for bail, although there may be other reasons behind that, I suppose.
So... deliberately ran her down and killed her. And hid her body and refusing to say where, thereby prolonging the agony of her family, depriving the victim of a proper burial, and unnecessarily adding tons of hard work to the job the police have to do. Wow. If they're right, what a horrible individual he is. I think I might prefer them to find her before he caves and gives up a location. I'd hate to see him become eligible for ANYTHING good by telling them. But of course, if they don't find her, I still hope eventually he confesses to the location. It must be so hard on her family, just knowing that she's still out there somewhere where she should never be.