It's obvious the cops messed up this investigation.
They could have arrested him when he returned without Gabby in her vehicle.
Then they claimed to have put Brian under surveillance and lost him from his own house.
Then where his bones were located its claimed that its near the entrance to the park, his parents claimed to have told the cops to look in that area early on in the search. His body was supposedly under water yet so far as I can tell his backpack, which contained a notepad, doesn't seem to have been in the water.
Something seems about fishy to me in how the cops are acting. There seems to have been a lot of blundering coincidences going on in this investigation.