One thing is certain :
If a police detective asked Ashley Biden, "Excuse me, Ms. Biden ... Did you write these entries in your diary?" and Ashley Biden said, "No." .... and then the detective asked her, "Has your father ever sexually abused you?" and she again said "No." .... and finally, if the detective asked, "Do you want this diary back?" and she said, "Yes." ..... then it was over. That is all of the investigating which can take place.
There is literally nothing else which can be done, because the information which became public from that diary, only did so because the diary was stolen. Anyone who knows a damn thing about the law understands that the police can not obtain information by way of theft. The diary was private property.
Now, is that how it went down? Maybe ... Maybe not. I don't know and neither do you.