I agree Mrs. Holmes. I don't think most police forces have the resources to spend or don't want to on some cases because they are a big hot mess. As a second factor in this case, the DA may not want to try and prosecute someone because of $$ they would spend on their defense and/or because they would need a lot more investigating to get someone convicted.
Having said all that, I believe it is often private attorneys and investigators who end up putting the necessary pieces together. If the attorneys in Rebecca's case can do that, which I think they can, I have high hopes someone(s) WILL be eventually convicted.
Also, sometimes someone eventually talks or comes forward. I have to wonder if someone were afraid they'd be thrown under the bus if that would happen here whether that is an LE investigator, a coroner or someone related to the perp(s) in some way.
We can be pretty sure there were things in the original LE files that we have never heard of too. It always boggles my mind when I hear about some of the things that were never made public in some criminal trials....