Of course there is a lot we don't know here. Caliber used would be helpful. What is the homeowners rep with the local police department?
I know this shouldn't matter, but if he's a dirtbag himself, the cops are just naturally going to be less enthusiastic about doing the proper investigation. Bias you say? Yep. Cops are human too, and if they've had to fight/chase/arrest the homeowner in the past, there may be a little "getting even" going on. Don't know that obviously, but without more facts it's hard to say.